Thailand’s two Thonburi class warships of WWII were very unique and interesting designs, but very little has been written about them.
The second ship of the class, HTMS Sri Ayudhya, was later sunk in one of the strangest situations of post-WWII naval history; a big-gun capital ship fighting in the downtown of a major inland city. Outside of Thailand even less has been written about that. So, perhaps this will be of value.
(The Thonburi class as they appeared during WWII.)
(The old dredge Manhattan, which lent its name to the failed 1951 rebellion which resulted in the loss of HTMS Sri Ayudhya.)
The two ships of the Thonburi class, of which HTMS Sri Ayudhya was the second, are in English normally called “coastal defense ships”. This was a type once popular in some Baltic navies with no analogy in the US Navy. They were not battleships, but not cruisers either, yet more advanced than a monitor.
Thailand’s interest in this style started with a 1920s order for two Ratanakosindra class ships from British shipyards. Essentially enhanced monitors, they were only 174′ long (about the same as a WWII Admirable class minesweeper) but had a 1¾” armor belt and two 6″ guns in single turrets.
(HTMS Ratanakosindra before WWII. Despite how it looks, the two single 6″ guns gave no stability problems on the small hull.) (photo via navypedia website)
(Both ships of this class, already obsolete, survived WWII and were kept in service. Here HTMS Sukhotai conducts bombardment during a 1957 amphibious exercise.)
The Royal Thai Navy considered the Ratanakosindra concept valid and looked to take it to the next level. Tenders were sent to shipyards in the UK, Italy, and Japan for a larger version.
deeper theories of the design: the “shell game”
Thailand was the only one of southeast Asia’s ancient empires to resist colonialism. This was not for lack of trying, as the British, Dutch, and French at varying times desired it.
(Thailand, or Siam as it was known, in orange on a 1920 map between British Malay, French Indochina, and British Burma. China at the time was nominally the Beiyang Republic but embroiled in warlordism. Taiwan was a Japanese possession and the Philippines a commonwealth of the USA. The Indies belonged to the Netherlands, and Singapore to Great Britain. Siam was the only stable independent entity on this whole map.)
During the 1930s the Thai government desired to make any future foreign colonization attempt as militarily unattractive as possible.
The Thonburi class would be key to this. These two warships would have guns commensurate to a medium cruiser. The Royal Thai Navy reasoned that for an overseas navy to overcome them, their 7.87″ guns would thus require two enemy heavy cruisers or battleships to be deployed out-of-area to southeast Asia.
By early 1935 when characteristics were being defined to prospective shipyards, Adolf Hitler was already in power in Germany and Benito Mussolini in Italy, and the world was rapidly building up seapower in arms races against perceived future threats.
What Thailand wanted was for the two inexpensive Thonburis to cause “a shell game” where any potential aggressor – the French, the Japanese, or the British – who sent heavy units to outgun the two Thonburis, would then be at a temporary numerical disadvantage of heavy cruisers / battleships in their “normal” operating areas against their “normal” perceived threat, be that the Italians, the Japanese, the Germans, or the Americans.
The Thais hoped that the need to deploy heavy warships to the Gulf Of Siam for a protracted period (and risk having them outright sunk) would be enough to dissuade any would-be colonizer.
The idea was not foolproof. It did not account for an aggressor slowly amassing a large number of lesser warships in Asia to “gang up” on the two coastal ships. This would factor into the loss of HTMS Thonburi during WWII. The concept also tied up a lot of money into ships with little offensive potential.
None the less, it was sound logic. It was a limited-budget navy smartly pairing up available hardware with geopolitical realities.
Thailand planned to complement them with two Italian-built Taksin class ships. These would have been full-fledged light cruisers for traditional high-seas combat.
Ordered in 1939, the unfinished hulls were later taken over by Italy for completion to an Italian design. Neither was ever completed and they were scrapped at Trieste after WWII.
These two ships were funded from a huge one-time naval outlay in 1935 for ฿18 million ($4,600,000 or slightly under $1 billion in 2022 American dollars) in three annual installments, above the Royal Thai Navy’s normal annual funding. Of this, ฿6.9 million was earmarked for Thailand’s first four submarines. The remaining ฿11.1 million had unpriced earmarks for a half-dozen new seaplanes but otherwise was free for the Royal Thai Navy to spend as it saw fit.
(The Watanabe WS.103S was Thailand’s version of the WWII Imperial Japanese Navy’s E9W1 “Slim”. The Thai version had features for submarine stowage omitted. One of these Thai planes was shot down by a F6F Hellcat during WWII.)
Japanese manufacturers won the budget’s “big prizes” (the two Thonburi class, the four submarines, and the seaplanes) but not the whole thing.
(Thailand already had two Italian-built Trad class torpedo ships and used the 1935 funding to buy seven more from Italy. They had British engines and were armed with a British QF 76mm gun, Italian Breda 20mm AA guns, and Italian 450mm tubes for Japanese unguided torpedoes. Two were sunk during WWII. During the Vietnam War the others were “Americanized” with surplus WWII US Navy guns as seen above. The last, HTMS Surasdra, decommissioned in November 1977.) (photo via 1976 edition of Combat Fleets Of The World)
The contract for the two Thonburi class ships was won by Kawasaki’s Kobe, Japan shipyard. Kawasaki’s shipwrights combined existing Imperial Japanese Navy systems and techniques, with foreign-made items at the Thai’s request, and offered the best price along with plankowner crew training and ongoing tech support. The order for the two ships was placed in late 1935 and the keels were laid in 1936.
(Main gun being installed aboard sister-ship HTMS Thonburi at the Kawasaki shipyard.)
Each of the two Thonburi class ships cost ฿2,863,500 ($705,510 or $14.6 million in 2022 American dollars).
This cost was absurdly low. Although there is no direct analogy a Brooklyn class light cruiser of the same time frame cost $18.5 million (฿74 million in that era’s money) when built. Obviously a Brooklyn was larger and more capable than a Thonburi, but none the less, the difference is staggering. The real difference is even larger still as the Baht was a weaker currency to the Yen than the Dollar.
(HTMS Sri Ayudhya in Japan before departing for Thailand.)
Without question, there was some “off the books” subsidization of Kawasaki’s contract from the imperial treasury. For Japan, this had the benefit of keeping Kawasaki employees busy honing their skills at building large warships. There was also a prestige factor, in that a Japanese company beat out competitors in Europe for a foreign contract.
HTMS Sri Ayudhya: basic description
(US Navy WWII guide for the Thonburi class. “Dhamburi” was an incorrect transliteration. Some specifications are slightly wrong. The error in the footnote “Both grounded in action….” is discussed later.) (Office of Naval Intelligence photo)
For what the Thais envisioned them to be, these two ships were well designed.
The Thonburi class measured 253′ x 47’4″ x 13’8″, and displaced 2,301t standard and 2,400t full with a crew of 234. The propulsion was two German-made MAN 5,200hp diesel engines turning two propeller shafts. The top speed was 15½ kts but the optimal cruising speed was 12 kts.
(HTMS Sri Ayudhya prior to WWII.) (Royal Thai Navy photo)
The main guns were carried in 2 x 2 turrets, with the aft turret a deck lower than the forward. Two lifeboats and two motorboats were carried. There was no radar and no sonar.
(The “wavy deckline” characteristic of Japanese naval architects prior to WWII can clearly be seen.) (drawing via thaigunship website)
The main armament was four Japanese 200mm (7.87″) 3rd Year 1-GO guns in two twin turrets, which had excellent firing arcs aboard HTMS Sri Ayudhya. This gun was originally the ship-to-ship weapon on the WWII aircraft carriers IJN Akagi and IJN Kaga, and was used on several WWII Japanese cruisers. It was a predecessor of the 200mm 3rd Year No.2 of the Myōkō class heavy cruisers. The Thonburis had the earlier gun but later turret style.
(Main guns on sister-ship HTMS Thonburi.)
(Forward main turret of HTMS Sri Ayudhya during WWII. The flexible cable run connected the in-turret plotter to the optical fire control device at the top of the superstructure.) (photo via NHK News Tokyo)
At 45° elevation the range was 15 NM and at 25°, 13 NM. The ammunition was separate type, with the propellant in 72 lbs cylindrical silk bags. The shell room was located under the propellant room in the magazine.
(A main gun aboard sister-ship HTMS Thonburi. Shells were hoisted up to the turret, rammed, and then propellant bags were hoisted up and rammed behind them. The loading tray then retracted and the breechblock was shut to put the weapon into battery. HTMS Sri Ayudhya’s gunners could get off about 4rpm.) (photo via thaigunship website)
Two types of Japanese ammunition were carried, the AP Type 5 and the Common Type 4, the latter having 16 lbs of HE inside but less armor penetration. Both weighed 242½ lbs.
The twin turrets were the Type D as used on the Imperial Japanese Navy’s Myōkō class heavy cruisers, with minor modifications. The Type D had a superimposed stereoscopic rangefinder which was smaller on the Thonburi class than on the Myōkōs. The turret rotation used an electro-hydraulic system that was rather sluggish at 4°/second. They had 1″ armor with 4″ faces.
(drawing via thaigunship website)
An interesting feature about the turrets on the Thai ships was the sheet metal “second roof”. This was not stand-off armor. It was intended as a comfort feature for the turret crew in the hot Thai sun; the idea being that convection would raise warmer air up and around the turret into the second roof, with a cooling effect. This did not really work well.
Even today, almost every non-Thai source incorrectly lists the secondary guns as Japanese Type 41 76mm guns. This is not correct, they were actually Bofors Model 1928s, a 2.95″ dual-purpose gun. This obscure Swedish-made gun was only used on a tiny handful of other WWII classes.The reason it was selected was that ammunition of this caliber was already in stock in Thailand.
These hand-loaded guns were already obsolete when HTMS Sri Ayudhya commissioned. There was no central fire control; each open mount was commanded locally. Movement was by handwheels, and the gun was visually aimed. The listed maximum surface-to-surface range was 8 NM which seems optimistic. The anti-aircraft slant ceiling was 34,780′ and these guns could fire nearly vertically. The shell only weighed 14 lbs and had no real armor penetration. Four were carried, two on each side amidships.
(The amidships area showing the two starboard 2.98″ guns and a twin Type 91 on the balcony above. A searchlight and the base of the starboard boat crane is also shown.)
The anti-aircraft weapons were originally Danish 20mm guns but during WWII, this was changed to twin Japanese Type 91 40mm guns. There were four, two amidships and two on the aft superstructure.
If these Japanese twin guns “look British” there is good reason; they copied concepts of the Vickers Mk.II 40mm gun. The Type 91 was belt-fed from 50rds snails. The effective range was 1 NM. These were not intended for surface combat but during the Manhattan Rebellion, that is what HTMS Sri Ayudhya‘s did.
The belt was 2½” thick tapering down on the ends. The horizontal armor plan was similar to the Ratanakosindra class. The main horizontal armor was 1½” on the second deck. Over critical areas, the weather deck above it was 1″. The internal barbettes were 4″. There was no anti-torpedo protection.
(HTMS Sri Ayudhya)
Some big WWII ships, like France’s Dunkurque class or Great Britain’s Renown class, followed “fight-or-flee logic”: the ship could outrun any opponent it didn’t outgun or out-armor, and could outgun anything faster than itself. The Thonburi concept did not have this luxury, as battleships and heavy cruisers could both outmatch it in firepower and armor, and were still faster.
The brief Franco-Thai War was a side conflict to WWII during late 1940 / early 1941. After Germany occupied France in 1940, French Indochina went to the Vichy French side but was in a bad situation. With Japanese troops already on its territory, it could not side with the Allies, but it was cut off from help from the Vichy rump state in Europe as well. Thailand sought to capitalize on this by seizing territory in dispute since the 19th century.
(The RTAF’s Mitsubishi Ki-30 “Ann” attack planes fought the Vichy French. This one was photographed four months after WWII ended, with the prewar insignia again in use. The last Thai “Ann” was discarded in early 1951, shortly before the Manhattan Rebellion.)
The naval engagement of the war was the battle of Ko Chang, fought amongst islets in the Gulf Of Siam.
The Thai flotilla was led by HTMS Sri Ayudhya‘s sister-ship HTMS Thonburi. It was escorted by two of the Trad class torpedo ships HTMS Chonburi and HTMS Songhkla, minelayer HTMS Nhong Sarhai, and a little patrol boat HTMS Thiew Uthok.
The Vichy French flotilla was lead by Adm. Jean Decoux. It was centered on the old light cruiser Lamotte-Picquet. This cruiser had eight 6″ guns and light armor, both inferior to HTMS Thonburi, but was bigger, faster, and more maneuverable. There were two 5″ gun frigates, Amiral Charner and Dumont d’Urville, and two obsolete sloops Marne and Tahure.
Aided by a reconnaissance seaplane, the French flotilla found the Thai force at 06:05 on 17 January 1941. The two Trad class ships were both anchored with cold engines, and were engaged by 6″ gunfire of Lamotte-Picquet. One was sunk and the other crippled. The captain of HTMS Thonburi, Cdr. Luang Phrom Viraphan, called away battle stations and sent a radio report to both the RTN headquarters at Sattahip and to the RTAF.
Unfortunately the French had previously found and destroyed the long-range radio relay ashore. The report to the RTAF was not received, while the one to Sattahip was delayed by being “daisy chained” by other Thai ships. Cdr. Viraphan used semaphore flags to order the minelayer and patrol boat to hide behind one of the rocky islets and not engage. This signals decision probably saved both ships, as Lamotte-Picquet had radio intercept gear.
HTMS Thonburi was at a disadvantage before the battle started. The gunnery officer, one of the best in the navy, had been put ashore overnight to measure tides in the area. It had been planned to retrieve him that morning, but this was now impossible.
At 06:40 HTMS Thonburi had closed to within main gun range. Due to the rapidly closing ranges, Lamotte-Picquet was itself almost simultaneously within its main gun range, and at 06:44 the two began exchanging broadsides.
At 06:48 the fourth salvo from Lamotte-Picquet scored a lucky hit, with a 6″ shell penetrating the superstructure armor directly beneath HTMS Thonburi‘s bridge. Cdr. Viraphan was KIA and much of the bridge crew was injured. The helm was destroyed and a fire started inside the superstructure.
HTMS Thonburi‘s navigator ran to the lower aft part of the ship, and kept HTMS Thonburi fighting by directly manipulating the rudder’s hydraulic ram to maintain steering.
Another hit from this salvo struck the aft turret, both damaging the turret and then shattering downwards where it clipped a water pipe, which resulted in the aft magazine flooding out.
A third 6″ shell of this same salvo penetrated a weakly-armored hull area and detonated in a bunkroom, starting bedding and clothing there on fire.
Tactics of both ships were hampered by the rocky Ko Chang islets, some of which are hundreds of feet tall, like mountaintops in the ocean.
In another stroke of bad luck, the forward turret’s rotation mechanism broke down. The guns could still elevate and fire, however to aim them would now require timing the target’s bearing with a turn. This made accuracy very poor for the rest of the battle.
With the captain dead and two fires burning, HTMS Thonburi had a respite at 06:55 when Lamotte-Picquet had to maneuver to avoid running aground. However the other four Vichy French ships, slower than the cruiser, were now in 5″ range and engaging HTMS Thonburi. HTMS Thonburi was returning fire with its hobbled one remaining main turret and also the 2.95″ guns, however those obsolete weapons scored no hits.
At 07:30 Lamotte-Picquet completed its maneuver and was again in 6″ gun range. The other four French ships disengaged and the cruiser again began scoring hits on HTMS Thonburi.
At 07:51 Lamotte-Picquet fired three torpedoes at HTMS Thonburi, of which all missed. By now the Thai warship had three fires burning, had slowed, and was starting to list to starboard. Adm. Decoux was concerned about Thai submarines possibly in the area, so the French ships departed.
By 10:00 HTMS Thonburi had taken on so much water that the weather deck was at the sea’s surface. The minelayer HTMS Nhong Sarhai took the burning ship in tow. HTMS Thonburi was listing so severely that HTMS Nhong Sarhai had to tie up to the port side, dragging the larger ship sideways, until it was over a sandbar near Cape Ngob.
At 11:00 the crew abandoned ship.
Another Thai warship, HTMS Chang, arrived at Cape Ngob and attempted to tow the smoldering hulk back to Sattahip. Under tow, HTMS Thonburi again started to list. HTMS Chang tried to run it aground, but it capsized in very shallow water.
HTMS Thonburi was later righted, raised, and towed to Bangkok with its long-term future pending.
During the battle HTMS Sri Ayudhya sortied as soon as the radio reports were relayed, but arrived too late.
the Japanese occupation
On 8 December 1941 (concurrent with the Pearl Harbor attack on the other side of the international dateline) Japan launched an invasion of Thailand. Fighting lasted only about 12 hours. Prime Minister Plaek Phibunsongkhram (who a decade later would later figure into HTMS Sri Ayudhya‘s destruction) figured the situation hopeless and requested an armistice. On 25 January 1942, Thailand declared war on the USA.
President Roosevelt considered the declaration of war null and void. Congress agreed and refused to acknowledge it, instead declaring Thailand a “Japanese-occupied neutral” and Phibun, as Plaek Phibunsongkhram was known in America, to be a quisling.
(The RTN’s air wing received six Aichi E13A “Jake”s as Japanese military aid. One shot down an American B-24 Liberator during WWII. They were discarded a year after WWII ended.)
There was no role for HTMS Sri Ayudhya to play in the rest of WWII. Given the defensive nature of the Thonburi design, there was little Allied threat in 1941 and 1942. By the end of 1943, the strategic situation flipped dramatically and now there were so many American submarines and mines in the Gulf Of Siam that a mission was no longer possible.
In mid-1945, the Thai army was planning a massive revolt against the waning Japanese. However WWII ended on 2 September 1945 before this could happen.
a mixup of names
In 1941 Vichy French naval intelligence in Saigon issued a muddled report that both HTMS Thonburi and HTMS Sri Ayudhya had been disabled, one by combat and the other by running aground. In reality HTMS Thonburi had suffered both fates and HTMS Sri Ayudhya neither.
When this was intercepted by US Navy intelligence, it was again mistakenly altered to both ships having been damaged in groundings but refitting and expected to return to service.
(The burnt-out HTMS Thonburi being patched up in Bangkok during WWII.)
Later during WWII Allied planes spotted the cosmetically-repaired HTMS Thonburi pierside but not HTMS Sri Ayudhya (it was on a training sortie that day) and the Allies now theorized that HTMS Sri Ayudhya had been destroyed by the Vichy French in 1941 and not HTMS Thonburi, instead of the other way around.
This third error was rectified very late in WWII however it had been disseminated so widely that some sources continued repeating it. As late as the 1950s, some otherwise-reputable defense publications were still swapping the ship’s names.
HTMS Sri Ayudhya between WWII and the Manhattan Rebellion
There was no effort to modernize HTMS Sri Ayudhya after WWII. The 1930s “warship shell game deterrent” concept, now worthless, was baked into the design and precluded using it for much else.
Sister-ship HTMS Thonburi was never again fully operational. After being patched up in Thailand during WWII, it was planned to have Kawasaki make full repairs once Japan won. As this never happened, it was instead retained as an inport tender and administrative barge.
The Thai army, navy, and air force all had legacy Axis-made systems after WWII. The RTAF was the fastest to discard these, as warplanes in the 1940s “turned a generation” every few years and in any case were limited by fatigue life of the airframe.
(A Nakajima Ki-43 “Oscar” fighter two years after WWII. During WWII the Japanese felt the red-white-blue Thai insignia looked too close to the British insignia and made the RTAF use a Japanese “rising sun” with an elephant superimposed. The last RTAF “Oscar” was withdrawn in 1949.)
The army, which was the largest and politically strongest branch, had a bewildering mish-mash of rifles, artillery, and tanks but slowly began to standardize on WWII-vintage American gear during the late 1940s. This greatly accelerated when Thailand entered the Korean War alongside the USA in 1950.
The navy was the slowest to discard Axis-origin gear. Warships are expensive things with long expected service lives. Thailand is an industrialized nation, and had at least a limited ability to reverse-engineer Italian and Japanese spare parts.
(Taken during a late-1950s fleet review, this photo shows one of the two 1920s-vintage Ratanakosindra class with an Italian-built Bangrachan class minelayer in the background. The two Bangrachan class ships were funded out of the same special budget as HTMS Sri Ayudhya and were completed in 1936. They decommissioned in 1980.)
(The WWII lines of HTMS Sichang look a bit out of place against the skyline of modern Singapore in 1978. This Japanese-built attack transport commissioned in 1938 and fought in both WWII and the Korean War. HTMS Sichang decommissioned in 1983.)
So HTMS Sri Ayudhya was by no means the only Axis-built ship still in the Thai fleet in 1951. Thailand had little trouble keeping these ships going – with one exception.
(HTMS Sri Ayudhya and HTMS Matchanu.)
As part of the special 1935 budget, Thailand purchased four Matchanu class submarines from Mitsubishi in Japan. They all commissioned together on 19 July 1938, the same day as HTMS Sri Ayudhya.
The Matchanu class was a private design by Mitsubishi. Thailand was the only customer. They had four Japanese Type 44 No.2 torpedoes with no reloads, and had no sonar, no radar, and only a basic radio. None of the four sank any ships during WWII.
After WWII the Royal Thai Navy retained them to keep submarine crews trained until something better became available. Because submarines are such a specialized thing, this was much more expensive than surface ships, even physically larger vessels like HTMS Sri Ayudhya. WWII American Mk14 and Mk16 torpedoes were incompatible and preservation of the remaining WWII Japanese torpedoes was another expense.
The batteries were especially problematic. Japanese lead-acid submarine batteries of WWII were a rubber jar type, not made anywhere after WWII and with the submarines being incompatible with American batteries. The batteries had an 8 year lifespan but by 1951 were 13 years old. During the late 1940s a huge amount of money was spent on a failed effort by Thai industry to develop a replacement. The submarines in general, and the battery project in particular, were considered a wasteful mess by the army.
the Manhattan Rebellion: origin of the incident
Plaek Phibunsongkhram, or Phibun as most Americans knew him, had been removed from office late in WWII. After the war he was tried as a collaborator but acquitted. Phibun returned to power as prime minister via a November 1947 military coup.
(Phibun greatly toned down his generalissimo-type styles of WWII and presented himself as a modern ally against communism.)
By 1951 Phibun was losing citizen support and within the military. He had already fended off coup attempts in 1948 and 1949.
During WWII the half-willing alliance with Japan had given the Thai military some positives, in the form of free Japanese weaponry and training. One negative lesson carried over past WWII in Thailand, was the intense WWII inter-sevice rivalry between the Imperial Japanese Army and Imperial Japanese Navy.
In Thailand, this went out of control in the late 1940s. The military was intricately involved with Thai politics, and the air force, army, and navy not only saw themselves as outright political opponents. The sides even escalated into a ideological quarrel, with the army being more “conservative” and the navy more “liberal”.
By 1950 the Royal Thai Navy was frustrated at the government’s authoritarian tone and the lack of funding for new warships, while the army was equally frustrated with the navy’s seeming lack of discipline and budget overruns, particularly the submarine battery fiasco.
Thailand is bigger than California and has one of Asia’s longest coastlines. None the less by 1951 the hyper-politicization of the military meant that 40% of the naval manpower was 20 miles inland, inside metro Bangkok.
(Bangkok was already on a semi-war footing in 1951. The Korean War, which Thailand participated in, was underway. On the other side of the nation’s eastern and southern borders, France’s Indochina War and Britain’s Malay Emergency were being fought. This 1951 photo shows a Type 75 in Bangkok. This Swedish-designed WWII anti-aircraft gun remained in use into the mid-1950s.)
In late 1949 a secret faction of progressive officers called “Save The Nation Group” formed. They were overwhelmingly navy and marine corps, but included (at first anyways) some army. Their first attempt to seize power was to have been in 1950, when they planned to arrest Phibun at the sending-off ceremony for Thai infantry going to the Korean War.
This was called off at the last moment when it looked likely to fail. (It would have also been a propaganda bonanza for North Korea.) This fiasco resulted in some Save The Nation Group officers losing interest, or even secretly turning against the group.
A better opportunity seemed to present itself during the summer of 1951 at the handover of an old American dredge, the Manhattan.
the dredge Manhattan
For starters, contrary to how it is sometimes still presented today, this ship wasn’t “formerly USS Manhattan”. This Manhattan was never in the US Navy.
Manhattan was built by Maryland Steel Company in 1904 at a cost of $341,577 ($10.3 million in 2022 dollars) and acquired by the US Army Corps of Engineers in 1907. An American law of 1824 allows the US Army Corps of Engineers to assist in things not strictly of a military nature, such as surveying levees and keeping waterways navigable. Non-milspec ships were often acquired.
(This photo of Manhattan is undated but was probably taken during WWII. The Corps of Engineers castle emblem is on the funnel, or smokestack.)
Displacing 2,790t empty, Manhattan measured 288′ x 47’6″ x 20’2″ and had a metal hull with wood superstructure. Manhattan had a “shift crew” of 19 men, but there were accommodations for three work shifts. The main (propulsion) lineup had four Coatesville boilers and two 900hp reciprocating engines for a maximum speed of 10 kts empty or 7½ kts with a full load of mud.
The secondary engine room powered the dredge suction pumps. It had two 350hp engines which fed off the main steam supply. Manhattan was a hopper-type dredge, meaning it sucked up sand and mud off the seafloor; as opposed to bucket-type dredges which are also suitable for hard bottoms but work slower. The hopper held 68,310 ft³ of mud. When full, the ship moved out of the navigation lanes and dumped it back overboard. The pipe was 20″ in diameter and could operate down to 45′.
Manhattan served the Corps Of Engineers during both world wars. By the end of WWII in 1945, Manhattan was overdue for replacement. Increased military funding with the start of the Korean War in 1950 finally allowed the Corps of Engineers to retire it.
The dredge passed from to the Economic Cooperation Administration. The ECA was set up in 1948 to administer the Marshall Plan abroad. It was led by Paul G. Hoffman who had run the Studebaker car company’s wartime production during WWII. The Manhattan transfer was one of the final ECA projects, as it disbanded later in 1951.
The ECA provided the dredge to Thailand as a civil gift and it was not for naval use. The goal was to deepen and widen waterways so larger merchant ships could call on Thai ports. Manhattan was towed through the Panama Canal and across the Pacific by a chartered Dutch tugboat. A skeleton American ECA civilian crew remained aboard.
the Manhattan Rebellion and sinking of HTMS Sri Ayudhya
When Mahnattan arrived at Bangkok in June 1951, the possibility of a naval coup attempt was not far-fetched.
Invitations to the handover ceremony received an unusually large number of “unable to attend” replies from senior officers who were probably tipped off ahead of time.
The revolt was led by LtCdr Manat Charupha. Also in on the plot was the captain of HTMS Ratanakosindra, several commanders of the Royal Thai Marine Corps, and other relatively insignificant naval officers.
The plan, which was goofy and half-baked at best, was to arrest the prime minister aboard the Manhattan and bring him aboard HTMS Sri Ayudhya. Under LtCdr Charupha’s command the ship would proceed south on the Chao Phraya river to Bang Na, which in 1951 was 9½ miles downstream from Bangkok. The coup would be announced there. If Phibun’s army-led government surrendered, the coup would end and he would be released, otherwise HTMS Sri Ayudhya would proceed down the river another 8 miles to open ocean, and sail for Thailand’s distant southern panhandle to form a rebel government.
At 11:00 on 29 June 1951, LtCdr Charupha held a final meeting with the other plotters and their units began positioning around Bangkok.
(Obviously Bangkok in 2022 is somewhat different than in 1951; there were fewer bridges across the Chao Phraya and some of the highlighted buildings no longer exist.) (map via Bing)
Military and civilian guests began arriving to the Manhattan around 14:00. The guests included wealthy European and American expatriate civilians, and Indonesia’s defense attache. Manhattan, still with the American civilian crew aboard, was moored at the Tha Rat pier on the east riverbank, almost directly across the river from the RTN’s administrative offices and fuel farm on the west riverbank.
(Civilian guests arriving.) (photo via Khaoso News)
The handover began at 15:00 with a Buddhist priest blessing the ship. The two national anthems were played as the flags changed. At 15:30 Phibun was to give his speech.
As Phibun began his speech, LtCdr Manat Charupha and two accomplices approached him with Thompson submachine guns and informed everybody that the prime minister was under arrest. They escorted him past the confused and worried guests to Manhattan‘s gangplank.
(This photo captured LtCdr Manat Charupha with his tommygun amongst guests.)
Also at precisely 15:30, far from the river on Bangkok’s west side, conspirators used grenades to knock the city’s then-only civilian radio station off the air. At the same moment, a different unit seized the Wat Liab power plant on the south side. Bangkok’s telephone switchboard was in this building, and it offered a vantage point to the Memorial Bridge’s east end, with the bridge being key to the coup.
(Memorial Bridge, also called Rama I Bridge, was built in 1932. Prior to the 1970s the center span was a drawbridge to allow big ships upriver into downtown. The first target for the very first B-29 Superfortress mission during WWII was Memorial Bridge. The B-29s missed but it was later damaged in 1945.)
Also at 15:30 sailors at the RTN’s Signals Division headquarters took up arms. On the other side of the river, the Royal Thai Marine Corps barracks activated its preexisting riot control plan, and rebelling marine units dispatched along the west riverbank and at the Memorial Bridge’s west end.
As the coup leaders and Phibun came ashore off the Manhattan, a LCM landing craft approached with its cargo bay covered by a tarp. During WWII, these simple amphibious types brought American troops ashore at many of the biggest battles. Now in 1951, the RTN used them as water taxis inbetween the various naval posts in the city.
When the tarp was pulled off, the LCM was full of armed men. They secured the area around the pier which Manhattan was tied up to. The coup leaders and Phibun got into the LCM which immediately headed upriver.
(photo via Royal Thai Naval Institute)
The first violence occurred at this point. According to witnesses, somebody shouted an insult and sailors on the LCM responded by spraying Manhattan‘s hull with submachine gun rounds.
The LCM with the coup leaders and their hostage sailed ¾ of a mile upriver to what was then the RTN’s main operations quay, Wat Rachathiwat. They all quickly boarded HTMS Sri Ayudhya.
At 16:00 HTMS Sri Ayudhya cast off lines and headed south downstream. Here is when the problems started.
The whole coup hinged on having Memorial Bridge secured and raised no later than 17:00. Two marine corps units were assigned this task.
(HTMS Sri Ayudhya passing under Memorial Bridge during happier times.)
The RTMC units apparently got cold feet at the last moment. When HTMS Sri Ayudhya reached Memorial Bridge just before 17:00, it was still lowered. The reluctance of the marines may not have mattered anyways, because an alert Thai army unit found the utilities box which fed electricity to the drawbridge bascules and disabled it.
This effectively doomed the coup. HTMS Sri Ayudhya, with the hostage prime minister aboard, was now trapped in downtown Bangkok.
As HTMS Sri Ayudhya loitered north of Memorial Bridge, the Thai army and police ejected the rebel sailors from the Wat Liab power plant overlooking it.
The entirety of the army, air force, and police opposed the coup. Around 20:00 LtCdr Manat Charupha received a disturbing radio report from the Wat Rachathiwat base upriver, a RTMC rifleman unit had arrived but was not inclined to help the coup. This meant that part of the navy was also not going along with it; and also meant that it might not be safe for HTMS Sri Ayudhya to return there.
By now, HTMS Sri Ayudhya was beginning to receive sporadic pot shots from rifles and carbines of soldiers and policemen on the riverbanks. The RTAF made its first response, when Spitfires made an ineffectual strafing run on the ship.
(Spitfires acquired from the UK replaced Thailand’s last “Oscar”s in 1949. The RAF insigina is faintly visible on this one. They were replaced by F-86 Sabre jets in 1960.)
As night fell loyalist soldiers controlled Memorial Bridge’s east end. Rebel forces held the west end. The center span was a no-man’s-land where gunfire was exchanged throughout the night. Army troops continued to take shots at the loitering HTMS Sri Ayudhya as well, with sailors aboard the ship responding with rifles from the small arms locker.
The bulk of the Royal Thai Navy was at Sattahip, on the Gulf Of Siam. Most of the ship’s captains were genuinely unaware of the plot. They radioed Adm. Sindhu Kamolnavin, CinC of the fleet, for orders. The admiral was “fence-sitting” to see how the coup would go, and did not reply one way or the other. So the rest of the fleet did not come to HTMS Sri Ayudhya‘s aid.
Little more happened during the night of 29 – 30 June. The coup leaders apparently forgot that the Bangkok Post Office had an AM transmitter, and the government began using it to offer their version of events to the city.
At 00:00 on 30 June a message from Phibun, recorded aboard HTMS Sri Ayudhya and relayed by the RTN Signals HQ on the city’s west side, appealed for negotiations by the army. Obviously made under duress, his appeal was denounced by the Post Office radio. At 01:20 the RTAF radioed HTMS Sri Ayudhya that it intended to bomb the ship unless Phibun was freed by 05:00. LtCdr Manat Charupha felt this was a bluff, in that no serious attempt to sink HTMS Sri Ayudhya would be made with Phibun as hostage aboard.
It was not a bluff. As the sun came up on 30 June, at 05:40 army units along the east riverbank, who had massed overnight, started pouring small arms fire onto the loitering HTMS Sri Ayudhya.
(Infantry at the flower market engaging HTMS Sri Ayudhya on 30 June with WWII Thompson submachine guns, which Thailand called the Type 88.)
The Thompson is one of the most famous firearms in history and needs little introduction. Thailand used the M1928A1, M1, and M1A1 models, all called Type 88. In Thailand’s army firearms are designated by the last two digits of the Buddhist year they were approved. This created a headache for 1950s quartermasters as not only the tommyguns, but also the M1903 Springfield and M1 Garand rifles, the M1918 BAR, and the M1919 and M1917 machine guns were typed to the year relations with the USA were reestablished: 1945 / 2488. All these guns were “Type 88”.
(A Type 77 gunner pours rounds onto HTMS Sri Ayudhya on 30 June. The helmet is the Thai M-26, similar to the WWII French Adrian. Thailand also wore WWII Japanese Tetsu-bos and American M1 pots in 1951.)
The belt-fed Type 77 entered service in 1934. It was chambered for the Thai T-66 8x57mm(R) cartridge. The Manhattan Rebellion was the last use of this WWII machine gun.
(Infantryman with a Type 47/66 carbine takes aim on 30 June. The helmet is the aforementioned M-26.)
The Type 47/66 carbine started off as the R.S. 123 Short Rifle, of which 10,000 were made by Tokyo Arsenal in 1904 chambered for the obsolete T-44 8mm cartridge. It had a Mauser action but certain Japanese features, such as a dust cover and ovular bolt handle. During the 1920s these were rechambered to the T-66 8x57mm(R) cartridge, restocked, and received a modified rear sight and bayonet lug. Besides the 10,000 rebuilds, 3,000 more were made new in Thailand and they served into the 1960s.
For HTMS Sri Ayudhya on the morning of 30 June, the small arms bullets were (structurally speaking) like flies to an elephant. They did however create problems in that the secondary and tertiary guns lacked gunshields, and were fed by scuttle-doors. One of HTMS Sri Ayudhya‘s fires was started by a lucky bullet setting off a Bofors 2.95″ round while an ammo scuttle was open.
A bigger problem for HTMS Sri Ayudhya was that around 06:00, rifleman companies from outside the capital who had arrived overnight took up positions on the riverbanks. They brought with them mortars.
The M2 was the standard American 60mm mortar during WWII and was adopted by Thailand in the late 1940s. The 2¾ lbs bombs did not individually threaten HTMS Sri Ayudhya but repeated hits by these caused a lot of cumulative damage to the ship’s upperworks. They were also used in the urban fighting, including setting ablaze the RTN’s gasoline depot.
Mortars, riflemen, and machine guns took up positions at the east riverbank flower market near the Memorial Bridge’s east end.
HTMS Sri Ayudhya was returning fire with the 40mm AA guns and 2.98″ secondary battery. The four 7.87″ main guns went unused. In theory these WWII Japanese weapons could fire at 0° elevation, but here the shells would have impacted only 80 yards in front of the muzzles, presenting its own issues.
As the loitering HTMS Sri Ayudhya was a sitting duck, the ship turned around in the Chao Phraya river. This was not easy as HTMS Sri Ayudhya was 253′ long and the Chao Phraya was only about 365′ wide and had a current. HTMS Sri Ayudhya managed to make a tight 180° turn and head upstream. It did not get far.
The RTAF made good on its overnight promise and a flight of T-6 Texans attacked HTMS Sri Ayudhya around 08:00.
(T-6 Texan of the RTAF.)
The T-6 Texan was the best trainer of WWII. While not designed for combat, it could be fitted with machine gun pods or small bombs. They began replacing Thailand’s Tachikawa Ki-55 “Ida” trainers in 1948. On 30 June 1951, they carried M30 bombs.
(M30 bomb) (photo via IMA-USA)
This American WWII bomb weighed only 100 lbs. The RTAF later said that they selected it because it was the smallest in inventory, and they intended the M30s only frighten HTMS Sri Ayudhya‘s crew with the tough ship shrugging off any hits. That may or may not have been true. In any case, the Texans bombed from 2,000’ altitude. Some of the M30s fell on civilian buildings along the river, a few hit HTMS Sri Ayudhya to little effect, but one made a freak impact directly on a topside ventilator.
Its blast went down the duct and set off HTMS Sri Ayudhya‘s aft 7.87″ magazine. Kawasaki designed the Thonburi class with a crude flash-trapping system, in that an explosion in either the turret, the shell magazine, or the powder magazine wouldn’t spread to the other two. It may have worked as former crewmen described the blast as “big firecrackers” indicating ammo detonating in short order, instead of the entire powder room going off at once as happened to USS Arizona at Pearl Harbor. It is also likely that the magazine was not full, as Thailand had not received any new 7.87″ rounds since 1945. In any case the explosion destroyed the engine room and started a large fire, in addition to one already burning. The ship began to list due to firefighting water overwhelming the bilge pumps.
(HTMS Sri Ayudhya on fire, passing the Wichaiprasit landmark.)
With no propulsion, HTMS Sri Ayudhya sat crippled in the river. It probably didn’t matter because at 09:55 the Wat Rachathiwat naval post was overrun, so HTMS Sri Ayudhya had nowhere to moor. By 10:00, the army had charged across Memorial Bridge and was fighting sailors and marines on the west riverbank, and also firing on HTMS Sri Ayudhya from both sides now.
At 13:00 HTMS Sri Ayudhya lost electricity, just after receiving a report that the Naval Signals HQ was being overrun. At 15:30 the T-6 Texans reappeared and scored another bomb hit. The abandon ship order was issued at 15:40.
Phibun was released by his guards and handed a life vest. He swam to shore with bullets whizzing overhead. He showed up at a police station, sopping wet, along with three HTMS Sri Ayudhya crewmen. The sailors were arrested and the prime minister taken to safety.
(HTMS Sri Ayudhya listing and on fire.)
By sunset on 30 June, the coup attempt had collapsed. LtCdr Manat Charupha managed to change into civilian clothes and buy a train ticket to Burma.
The abandoned HTMS Sri Ayudhya continued to list and smolder overnight. The ship sank on 1 July 1951, just as the final holdouts of the coup were surrendering.
(The abandoned HTMS Sri Ayudhya sinking on 1 July.) (official US Navy photo)
In defense publications, it is often said that consequences of the Manhattan Rebellion “….crippled Thailand’s navy for generations”, “….set the Thai navy back decades”, etc. This is, for the most part, not really true.
Not surprisingly the army and air force came down hard on the navy in 1951. Even though he had not participated, Adm. Sindhu Kamolnavin was fired on the principle of command responsibility. Some obvious culprits were arrested on 30 June and about 1,100 more on 1 July; so many that Bangkok National Stadium became a makeshift jail. Most were quickly released. Only 99 were charged and at courts-martial some were acquitted. Of those convicted, they were given amnesty six years later.
The Royal Thai Marine Corps was disestablished. The units did not disband, they just moved to army control.
The RTN’s air wing was disestablished with naval warplanes being discarded or absorbed by the RTAF.
(Six WWII SB2C-5 Helldivers delivered in April 1951 were taken over by the RTAF. They were called “Attacker Type 3” and when the RTAF retired them in the early 1960s, they were the last Helldivers in service worldwide.)
The four WWII Japanese-built submarines were ordered to decommission, which was done on 30 November 1951. The Royal Thai Navy retained them at a quiet anchorage near the Bangkok Naval Hospital in hopes that the army would forget about them, and they could then recommission.
The naval GHQ was moved from Bangkok to Sattahip and the navy’s ashore artillery was given to the army.
The decision on the marine corps was the first to be reversed. In July 1955, four years after the Manhattan Rebellion, the RTMC was reconstituted and put back under naval control.
(Marine unit during a mid-1950s exercise. The American M1/M2 carbine of WWII had now become standard.)
In 1962 the Royal Thai Navy was again allowed to operate aircraft.
(When South Vietnam collapsed in 1975, some South Vietnamese WWII-vintage C-47 Skytrains which had fled to Thai airfields were absorbed into the RTN’s rebuilding air wing. This one was still flying in 1995.)
The most damaging of the 1951 decisions was the submarines. The army did not forget about them, and repeatedly pressed the RTN to dispose of them once and for all. In 1953 they were sold to Siam Cement Company as scrap.
(The nameless US Navy WWII subchaser PC-570 was given to Thailand in June 1953 as HTMS Longlom. Here it passes the condemned submarines, one of which is being cut up. HTMS Longlom served until 1994.) (photo via navsource website)
Operating submarines is such a specific thing to any navy that once it stops, in only a few years the ability is lost and can’t be restarted other than from scratch. From the 1970s through the 2010s, Thailand repeatedly tried and failed to restart a submarine force. Only in 2018 was funding granted for submarines, expected to enter service in 2023 – 2025.
As far as the Royal Thai Navy overall, there was no army intent in 1951 to diminish it long-term.
(Only eighteen weeks after the Manhattan Rebellion, the Royal Thai Navy was again expanding. The WWII Tacoma class frigates USS Glendale (PF-36) and USS Gallup (PF-47) were transferred as HTMS Tachin and HTMS Prasae respectively. This was at their handover, with the Thai flag flying but still in US Navy markings. They served until 2000.) (official US Navy photo)
By intent or not, the inter-services rivalries faded away. Although there were numerous further military coups in Thailand, none would be framed in an army vs navy battle.
(The US Navy’s nameless LSM-333 put men ashore on Okinawa during WWII. In 1946 it transferred to Thailand as HTMS Kut. This ship could drop a tank platoon and half an infantry company directly into downtown Bangkok. If the Thai army was seriously worried about a repeat of the Manhattan Rebellion, as is sometimes claimed, it is doubtful they would have allowed the Royal Thai Navy to keep this ship in 1951. HTMS Kut decommissioned in 1990.) (photo by Tangkijjarak Phakphum)
Looking at the RTN in the 1950s, 1960s, and 1970s; there were a lot of WWII-vintage warships in the fleet but regionally, navies such as South Korea, the Phillipines, South Vietnam, Taiwan, etc were of a similar makeup during that time frame. Thailand’s neighbors, Myanmar and Cambodia, had fleets both more obsolete and smaller. Finally some of the legitimately obsolete WWII warships were in niche roles, and if they were cheap to operate, it did not make sense to replace them.
(HTMS Sukothai in 1970.)
As an example of this, the second Ratanakosindra class ship of the 1920s, HTMS Sukothai, served into the Vietnam War era as an offshore fire support vessel. Long since already paid for, HTMS Sukothai was basically just a raft to move two 6″ guns around by the 1960s and didn’t cost much to run, so there was no point in buying something newer. HTMS Sukothai decommissioned in 1971.
what happened to the Manhattan
On the first night of the Manhattan Rebellion, the civilian American crew had been hunkering below decks as stray bullets continued to hit the ship. At 23:00 they decided that the danger of leaving was no worse than staying aboard, and with one of the Thai guests stranded since the handover ceremony, left Manhattan in the only lifeboat not shot up. They rowed against the current until they were north of downtown, just as the sun was coming up.
A week later, they were allowed back onboard to collect their belongings, which had been looted in the meantime. Manhattan was riddled with bullet holes. All of the topside features and work boats were shot up, and the fuel tank had been punctured.
It took half a month to repair the dredge. In a low-key ceremony during August 1951 Manhattan was renamed Sandon II. It was operated until 1961 when it was sold to a Hong Kong-based company and renamed Yau Wing #4. This ship was scrapped in 1974.
(At Chanasongkram police station is the original bell of the Manhattan, removed when it was repaired. This is the only monument of the Manhattan Rebellion in Thailand.) (photo via Khaoso News)
final fates of the Thonburi class
The HTMS Sri Ayudhya wreck remained an eyesore in Bangkok for several years. It was big, heavy, and in narrow waters making salvage difficult. It was finally dismantled in 1958.
During WWII, probably nobody would have predicted that HTMS Sri Ayudhya‘s sister-ship HTMS Thonburi would outlast it by many years.
(HTMS Thonburi with two Klongyai class patrol ships alongside in 1962. These Japanese-built warships had been funded out of the same 1935 special budget. They were partially “Americanized” during the Vietnam War and served until 1976.) (official US Navy photo)
As mentioned earlier, HTMS Thonburi was structurally repaired during WWII but never again fully operational. After WWII HTMS Thonburi was used as an inport small ships tender, administrative barge, and floating barracks. It continued in this role until decommissioning in 1967.
The forward superstructure and a main gun turret were moved to the Samutprakam Naval Academy and installed ashore.
As of 2022 they remain there and are used for both ceremonial and basic training functions.