Bedcheck Charlie 1950 – 1953

The Korean War’s air combat is best known for the duels of MiG-15s and F-86 Sabres in the world’s first jet-vs-jet matchups. An unusual sideshow to that was North Korea’s use of woefully obsolete WWII types as night harassment planes. They were called “Bedcheck Charlies” by the Americans.

(North Korean Po-2 “Mule” which was used as a Bedcheck Charlie plane, just as the Soviets had done during WWII.) (artwork via Wings Palette website)

(The MBR-2bis, another WWII Soviet plane used by the North Koreans for Bedcheck Charlie missions.)

(Two of the WWII-legacy American answers to the problem: a F4U-5NL Corsair and in the background, a F7F-3N Tigercat.)

during WWII

The nighttime harassment concept was true to its name. Regardless of how much damage they caused, pinprick type bombing raids would deny enemy troops sleep and exhaust anti-aircraft units.

During the 1941 German invasion, the Soviet air force suffered horrendous losses. Ideas which would have been otherwise rejected gained currency, one being dedicated night harassment units. An early type selected was the Kharkiv KhAI-5, a 1930s tactical bomber.

KhAI-5s had been slaughtered in their intended role during 1941 and this was a way to wring residual value out of the obsolete survivors. This bomber was too big to be successful however.

A different approach which showed much more promise, was to use slow, flimsy biplanes for night harassment missions.

(R-5 being ground-started by a truck which attached to the propeller spinner.)

The Polikarpov R-5, an obsolete early-1930s scout bomber, was used successfully beginning in late 1941.

The most famous mount of Soviet night harassment missions was the Polikarpov Po-2.

Po-2s were tremendously successful in the role, and today 75+ years after WWII have become synonymous with it. In popular culture the most famous Po-2 unit was the 46th “Taman” Regiment, which the Germans called the Nachthexen (night witches) as the aircrews were female.

This Po-2 unit made its debut in June of 1942. As designed there was no armament; during WWII many received a ShKAS in the rear seat. This belt-fed machine gun fired the 7.62x54mm(R) cartridge at 1,800rpm.

(Po-2VS without ShKAS but equipped with bomb racks and snow skis during WWII.)

At first mortar shells or grenades were simply thrown out of the plane. Later during WWII, Po-2s were jury-rigged with crude racks for FAB-50 110 lb bombs. The U-2NLB version (one of three dozen variants of the Po-2) was built-for-the-purpose for night harassment missions, and had not only the ShKAS and bomb racks but also underwing rocket launchers.

The Soviets raised three dedicated night harassment regiments. The Po-2 was perfect for these missions, as it flew so slow and so low that it was difficult for Luftwaffe night fighters to intercept.

These missions were dangerous in any number of ways. The Po-2s approached their target very low in the dark and risked hitting trees or the ground. The Po-2 was about as uncrashworthy of a plane as can be imagined, and the Soviets did not issue parachutes to night harassment units until 1944. Due to the low altitudes and the speed differential between high-performance fighters and slow biplanes, it was challenging for Luftwaffe night fighters to intercept them but not impossible. Luftwaffe Fw-190 pilot Lt. Josef Kociok shot down three Po-2s in a single night.

In December 1942 the Germans recognized the cost-to-benefit ratio that night harassment missions offered the Soviets, and the Luftwaffe created its own units.

In 1940 Germany captured some Danish air force Fokker C.Vs intact. These Dutch-built reconnaissance biplanes were too obsolete for any other use than night harassment missions.

Long in the tooth towards the end of WWII, the Junkers Ju-87 Stuka was repurposed as a night harassment type. A hider was fitted over the engine exhausts and the Stuka’s characteristic wheel spats were removed, as streamlining for speed was no longer relevant and it made one less hassle on grass airstrips.

The Gotha Go-145 was probably the most prolific German night harassment type. Originally a mid-1930s trainer, the Go-145 had a top speed of just 114 kts. These obsolete biplanes began flying nighttime harassment missions in late 1942 and never stopped; with Go-145s flying some of the Luftwaffe’s final missions. The night harassment unit NSGr-3 in the encircled Courland Pocket still had 16 of these biplanes in active combat when Germany surrendered in May 1945.

The Pacific theatre was less amenable to this concept but during the Guadalcanal battle the Japanese flew nighttime harassers. One, a G4M “Betty” bomber, was named “Washing Machine Charlie” by American GIs as the sound of an individual “Betty” at very low altitude at night was reminiscent of 1930s Maytag gasoline-powered home laundry appliances.

In contrast to the Soviets and Germans, the Japanese tended to use standard frontline types instead of biplanes for nighttime harassment, but one of the latter was used, the Mitsubishi F1M “Pete”.

(The “Pete” was the final new Japanese biplane to enter service in 1941 and the last to leave production in 1944. Some were still in service at WWII’s end in September 1945.)

Although some Po-2s participated in the final assault on Berlin, the Soviet harasment missions had tapered off after the Oder River crossing in February 1945. Dedicated night harassment units were disbanded in October 1945, a month after WWII overall ended. By 1946 it was generally felt worldwide that this tactic was probably no longer valid in the forthcoming age of jets and radar.

the Korean War

In 1946 Soviet forces in Korea north of 38°N (the dividing line agreed upon with the Americans to the south) laid the groundwork for what would officially become the North Korean air force (DPRK-AF) in 1948.

By the end of 1949, the DPRK-AF still had some obsolete types (including some ex-Japanese warplanes) in inventory, but with 260 decent combat aircraft backed up by 190 second-line types, the DPRK-AF had quietly become a notable force. On 25 June 1950 North Korea launched a massive invasion of South Korea.

(Tachikawa Ki-54 “Hickory” of the DPRK-AF. During WWII the Ki-43 was an advanced trainer for the Imperial Japanese Army. The North Koreans used it as a transport during the first year of the Korean War. This one was captured by American troops.)

By late August 1950 North Korea had pushed the South Koreans and Americans into a small pocket around the southern port of Busan. The turning point was the 15 – 19 September 1950 amphibious landing at Inchon, which was a complete American victory and now required the DPRK-AF, already under strain, to fly sorties in all directions.

The DPRK-AF as it existed at the war’s start in June was greatly diminished by late October 1950, when the PLAAF (Chinese air force) entered the war with jets.

In the meantime both the Chinese and Soviets had started to train new DPRK-AF pilots, but this would take time – both to train them, and to deliver new planes. This period, late 1950 to mid-1951, was the lowest point for the DPRK-AF. A spent force flying in exile from Chinese airbases across the Yalu River, there was little it could do to help North Korean and Chinese troops on the ground.

Much like the Soviet air force at its nadir during WWII, DPRK-AF leadership was open to unconventional ideas, including the nighttime harassment concept.

In a nod to the Japanese “Washing Machine Charlie” (the same moniker was also sometimes used during the Korean War) flights of WWII, American GIs during the Korean War called these missions “Bedcheck Charlie” in that they arrived after lights out was called on base. They were also called “Hecklers”, the American military slang for enemy harassment action of any sort.

types flown

the Po-2 “Mule”

Overwhelmingly this was the main type North Korea used for Bedcheck Charlie flights; the same as the Soviets during WWII. North Korea had eighteen Po-2s in service when the Korean War began.

(North Korean Po-2 “Mule”.) (artwork by Thierry Dekker)

The Po-2 was an open-cockpit, two-seat biplane 26’10” long with a 37’5″ wingspan. It was powered by a Shvetsov M-11D air-cooled engine which used common low-octane automobile gasoline. The M-11D spun a two-bladed VIAM-B3 wood propeller. The maximum speed was 82 kts and the never-exceed speed 90 kts. The practical ceiling was only 6,561′ – for comparison, this was half the ceiling of the Red Baron’s Fokker Dr.1 triplane during WWI, and just a fifth of a A6M “Zero”s ceiling during WWII. The Po-2 was also a sluggish climber, taking 8 minutes to reach 3,300′.

The “Mule” (its Cold War-era NATO reporting name) was originally designated U-2, for uchebnyy or training in Russian. This was one role, but the Po-2 was designed as a “jack of all trades”, military and civilian. Its Soviet nickname was Kukuruznik, or corn duster, from a 1930s scheme to seed maize farms by air.

(A 1950s US Navy assessment of the Po-2. For whatever reason, this was not declassified until 2013. Mention is made of the type’s night harassment or “heckler” usage during the Korean War.)

This airplane was designed by Nikolai N. Polikarpov’s design bureau, more famous for the I-15 fighter of the 1930s Spanish Civil War. The designation was changed from U-2 to Po-2 in 1944, around the same time the design bureau shut down when Polikarpov passed away.

To call the Po-2 crude is an understatement. Behind the engine, the whole thing was wood, fabric, or cheap metal. The floor was light sheet metal. The upper cockpits and upper fuselage was plywood. The rest of the Po-2 was fabric stretched over wood frames. The wings were fabric, set upon stamped metal or wood ribs supported by wood spars. The tail was wood and fabric. The fabric control surfaces operated by cables and pulleys, some external to the airframe. There were few parts to begin with and many were common, for example much of an upper or lower wing could be interchanged.

(Some of the Po-2’s control surfaces were moved by cables external to the fuselage.)

The main landing gear was fixed. The tail gear, a metal-shoed wood skid, was linked by wire and pulleys to the rudder for extremely basic ground steering. The Po-2 could be landed at just 20 kts airspeed. The runway requirements were 311′ takeoff and 349′ landing. The Po-2 could use grass or dirt airstrips and during the Korean War, usually did.

(Cockpit of a Po-2 “Mule”.)

Any number of roles – artillery spotting, casevac, staff liaison, training, target sleeve towing, mapping, instrument calibration, and of course night harassment missions – could be undertaken and various Po-2s had wheels, snow skis, or floats for landing gear.

Polikarpov’s plane started production at the Leningrad Zavod #23 factory in 1929 and ran to 1952. Poland license-built some from 1946 – 1959. Somewhere around 30,000 Po-2s were made over these 30 years; the most-built biplane ever.

(The PLAAF (Chinese air force) was also a post-WWII recipient.)

The Soviets began phasing out the Po-2 in the 1950s but the type was exported around the communist world after WWII, including to North Korea.

(An ex-Soviet Po-2 delivered to North Korea between the end of WWII and the start of the Korean War.) (artwork from Avia Master magazine)

other WWII types used in these missions during the Korean War

While the Po-2 was the most common type, other aircraft flew Bedcheck Charlie missions as well.

the Ki-9 “Spruce”

The Tachikawa Ki-9 “Spruce” was an Imperial Japanese Army trainer during WWII. Both North and South Korea inherited examples of these biplanes inside their new borders in 1945, and both of the new air forces used them.

(Ki-9 “Spruce” of the ROKAF, or South Korean air force. The South only used Ki-9s until sufficient American-made trainers entered service.)

North Korea used Ki-9s as trainers before the Korean War and then as artillery spotters during the initial 1950 invasion of South Korea. After the mid-1950 reversals on the battlefield, some were used in ad hoc nighttime harassment missions but this was before the tactic became official DPRK-AF policy. During the American advance out of the Inchon beachhead, most were destroyed or abandoned. Much later during the war, a very small number (probably donated by China) were again observed.

(official US Air Force photo)

The above photo was taken in 1953 at Kimpo, or “K-14” as it was called by the United States. This had been the Imperial Japanese Army’s Keijo New Airbase during WWII when the Korean peninsula was Japan’s Chōsen province. Kimpo was overrun by the North Koreans on 28 June 1950 and some DPRK-AF Yak-7 fighters, formerly a WWII Soviet type, were based there. It was bombed by B-29 Superfortresses during the summer of 1950 and recaptured on 18 September.

The Ki-9 “Spruce” above was a Bedcheck Charlie recovered at Kimpo. It is unknown if it was shot down just prior to the photo or just a wreck that had been in the area for a while. The writing on the fuselage (“National Aviation University”) is in Mandarin and not Korean. This particular “Spruce” may have come from the former Mukden Aviation School in Shenyang, China. During WWII Ki-9s there trained both Japanese pilots and those of the tiny Manchukuo air force. The school was overrun by Soviet troops during the final weeks of WWII.

The boxcar likely dates to WWII as well. The symbol is the version of Korail’s corporate logo used between 1947 – 1954. Both Korail (South Korea) and Kukch´ol (North Korea) railroads are successor companies to Chōsen Government Railway which became defunct with the Japanese defeat in WWII. Both used ex-Japanese rolling stock into the mid-1950s.

the Yak-18 “Max”

When the huge “Bagration” operation of 1944 ended with a Soviet victory, Josef Stalin authorized the Yakovlev design bureau to craft a replacement for the UT-2 “Mink” trainer which he had previously forbidden as a non-urgent project. Yakovlev offered the all-wood Yak-5, the prototype of which flew in September 1944. After Germany’s surrender in May 1945, restrictions on the use of aluminum for non-combat types were lifted and Yakovlev remade the design. The bureau had the luxury of time as trainers would be irrelevant to the USSR’s planned entry into the Pacific war in August. Had urgency been put on it, the design may have been ready by then but the bureau chose to refine it as much as possible. Hence the prototype Yak-18 was not flown until 3½ months after WWII ended. Mass production began in May 1946. It received the NATO reporting name of “Max”.

(North Korean Yak-18 “Max”.)

The two-seat Yak-18 was 27’5″ long with a 34’9″ wingspan. Powered by an Ivchenko AI-14RF piston engine, it had a top speed of 160 kts and a ceiling of 16,600′. While some portions were fabric over aluminum spars, much of the plane was metal.

The USSR delivered twelve Yak-18s to North Korea in 1952. North Korean Lt. No Kum-sok, who defected with a MiG-15 jet fighter in 1953, told US Air Force debriefers that he had been trained in a Yak-18.

(North Korean Yak-18, this one having been delivered to South Korea via defecting aircrew. They told debriefers that this particular Yak-18 had been one of the planes involved in a Bedcheck Charlie raid against Inchon in June 1953.) (photo via Smithsonian Institution)

North Korea modified some Yak-18s for Bedcheck Charlie missions with two under-fuselage pylons for small bombs, as seen in the above photo.

the MBR-2bis “Mote”

Beriev’s MBR-2bis is all but forgotten today but with over a thousand in Soviet service during WWII, it was not a trivial type. They saw combat in the Black Sea and especially in the Arctic, where they hunted German u-boats trying to ambush lend-lease convoys as they neared their destination ports in northern Russia.

This seaplane was 44’3″ long with a 62’4″ wingspan. The fuselage was wood and the wings and other surfaces were fabric, wood, and light metal. The MBR-2bis was powered by a Mikulin AM-34N liquid-cooled engine set above the fuselage and turning a pusher propeller. The top speed was 148 kts and the ceiling was 16,100′. The “Mote” (its post-WWII NATO reporting name) was armed with an obsolete PV-1 machine gun in an open nose mount and a dorsal turret for a ShKAS, the same gun as the Po-2 carried. Six small bombs could be carried.

Beauty was not a strong point and the MBR-2bis’s WWII nicknames in Russian were “korova” (cow) and “letayushchiy saray” (the flying barn). Although it was not intended as an amphibian, during WWII some MBR-2bis crews made them such by simply bolting struts for wheels or skis onto the wood airframe.

(Soviet MBR-2bis during WWII.)

A concern of a wooden fuselage for a plane like this is rot. During WWII the Soviets stored them ashore. Various things were done to inhibit rotting, including putting heat lamps in their hangar and pressing porous bags of dry sand against the fuselage to suck moisture out of the wood.

During WWII coastal patrol was the “Mote”s main role but the USSR experimentally used some MBR-2bis planes in the night harassment role, with surprisingly good results.

Many survived WWII. By the late 1940s they were reassigned to secondary tasks like rescue or fisheries control. Russian records indicate that nine “Motes” were exported to two countries. Finland used five so by definition, this meant that North Korea received four.

(Scale model of a MBR-2bis with DPRK-AF insignia. At least in the unclassified realm, there are actually no known photos of this plane in North Korean markings.)

However American intelligence during the Korean War indicated the DPRK-AF only had three. Its possible that one crashed very early on, or, that the intelligence was simply wrong.  These were based on North Korea’s east coast where they were assigned to nighttime harassment duties.

One interesting thing is that American intelligence, throughout the Korean War, referred to the MBR-2bis as “Blochividan MBE-2”, a non-existant type. How the error originated is unknown.

the Tu-2 “Bat”

Strictly speaking Tupolev’s Tu-2 “Bat” might not belong here as unlike the types above, the Tu-2 was not an obsolete castoff. The “Bat” (its NATO reporting name) had been a successful medium bomber during WWII and was good enough to be retained in service into the 1950s.

The Tu-2 was 45’3″ long with a 61’11” wingspan. It was powered by two Shvetsov ASh-82 air-cooled engines and had a maximum speed of 285 kts with a 29,900′ ceiling. It could carry 1½ tons of bombs internally or 2½ tons externally, or some combination thereof.

(North Korean Tu-2 “Bat”.) (artwork via Wings Palette website)

The Soviets provided Tu-2s to North Korea after WWII and during the initial 1950 invasion of South Korea, they were used in their intended mission as daylight bombers and tactical support aircraft. After American jet fighters started to appear in greater numbers, it became too hazardous to continue using the Tu-2 in this way and they were assigned to nighttime missions, some of these being traditional in nature and others, solitary harassment-type flights.

history of Bedcheck Charlie missions during the Korean War

The first North Korean nighttime harassment missions started during June 1950, usually just ad hoc and ineffective nusiance raids. One of these was shot down by a B-26 Invader. The first notable success came on 28 November 1950 when a single Po-2 attacked an airfield near Pyongyang; the North Korean capital having previously been overrun and occupied by U.N. forces. It destroyed several F-51 Mustangs (the post-1947 designation of the WWII P-51) on the ground.

The ordnance which Bedcheck Charlie planes used varied. The FAB-50, a 110 lbs Soviet bomb, was common.

(There were actually three weapons designated FAB-50 by the Soviets during WWII. The one above was a teardrop-shaped 110 lbs bomb of welded steel made midway and later during WWII. Another type was a more traditioanal bomb shape, but in one cast iron piece, made earlier. Both had a TNT filler and simple impact fuze. The third type was Romanian howitzer ammunition captured at Stalingrad and repurposed as harassment bombs. The North Koreans could have received either of the first two types. The FAB-50 designation was later reused during the Cold War for an unrelated modern bomb.)

It is possible some leftover Japanese Army Type 94 bombs, which were similar to the FAB-50, were used. Other times mortar rounds, artillery shells, or WWII anti-personnel bombs were used by the Po-2. The Tu-2 “Bat”, which was a de jure bomber by design, naturally had a wider range of options. The ShKAS carried on the rear seat of the Po-2 “Mule” was not as effective as might be imagined. The ShKAS was not a particularly great machine gun to begin with and prone to jamming due to its excessively high rate-of-fire. To use it for strafing required the biplane’s pilot to turn and bank sharply to one side which could present a problem with the plane flying so low in the dark. Some North Korean Po-2s were lacking the mount anyways. On one instance with a Po-2, GIs on the ground reported hearing the distinctive report of a “burp gun” (the WWII Soviet PPSh-41 submachine gun) being fired from the biplane, presumably by the observer leaning out of his cockpit.

The Bedcheck Charlie phenomenon gained traction during the summer of 1951. On 26 May 1951, six Po-2s attacked the “K-14” airfield near Inchon. They dropped at least four FAB-50s and eight “50 lbs artillery rounds”. As was usually the case their aim was horrendous but in a stroke of luck, one hit an aviation fuel pipeline and another hit an ammunition pallet.

A week later, another small group of Po-2s attacked “K-6” near Pyongt’aek, accomplishing nothing other than waking everybody up.

(North Korean Po-2 Bedcheck Charlie in 1951.) (artwork via Wings Palatte website)

On 17 June 1951, the concept scored its first really big tangible success. A lone Po-2 attacked Suwon AFB, destroying a F-86 Sabre jet fighter and heavily damaging others. The ordnance was described as leftover WWII anti-personnel bombs.

(Burned F-86 Sabre at Suwon AFB on 17 June 1951.) (photo via Leo Fournier)

There were other missions flown by the Po-2s during the summer of 1951, usually lone planes and usually causing little damage but fatiguing American troops. During autumn and winter of that year, the Bedcheck Charlie flights seemed to taper off.

During the summer of 1952, Bedcheck Charlie missions resumed in intensity. One frequent target was Cho-Do. This North Korean island was occupied by the Americans throughout the Korean War, as it was the ideal location for an air search radar looking north towards “MiG Alley”, a navigation beacon for B-29 Superfortress bombers, and HH-19 Chickasaw rescue helicopters to retrieve airmen who bailed out over the Yellow Sea.

(map via Bing)

North Korea had no ability to recapture the island and by 1952 it was too dangerous to fly propeller bombers in the daytime. However they moved long-range artillery to the coast and bombarded Cho-Do, and it made the perfect target for harassment by Bedcheck Charlies.

On 5 September 1952, six Po-2s dropped 14 small bombs. They all missed and instead landed on Cho-Do’s civilian town. Po-2s came again in various numbers or alone on 26 November, 5 December, and 10 December; each time causing little appreciable damage but exhausting the island’s AA unit when constant alert status and false alarms of incoming raids were added in.

Elsewhere, installations around Seoul were harassed by the North Korean biplanes during the late summer and early autumn of 1952.

The last big flurry of Bedcheck Charlie missions, and the heaviest concentrations, happened from February to July 1953. The ground war had largely become a stalemate with the front lines more or less static so it was easier to plan nighttime harassment missions.

On 15 April 1953, a small group of Po-2s hit Cho-Do island for the fifth time. This time the biplanes were successful, destroying some American equipment on the ground and killing two soldiers.

On the night of 16 / 17 June 1953, Inchon was hit by one of the most spectacular Bedcheck Charlie raids of the war.

(North Korean Yak-18 in 1952, the first year the “Max” was in DPRK-AF inventory. This was possibly one of the same planes in the 1953 mass Bedcheck Charlie attack against Inchon.) (artwork via Wings Palatte website.)

A swarm of fifteen planes (three Yak-18s and a dozen Po-2s) attacked the American airbase. One of them hit the fuel dump, starting a massive fire which consumed 5½ million gallons of jet fuel.

Another massed-type Bedcheck Charlie raid, which ended up being the final one of the war, was mounted against Seoul in mid-June. Here again the total number of planes was fifteen; being a mixture of Po-2s, Yak-18s, plus one or two La-11 “Fang” fighters. The La-11s may have been attached in the hopes that they could ambush American night fighters sent up to intercept the slow Bedcheck Charlie types.

(The Lavochkin La-11 “Fang” was a 1947 offshoot of the La-9 “Fritz” which was designed during WWII but arrived several months too late for WWII combat. Together they represented the USSR’s final piston-engined fighters. The La-11 was used extensively by the Chinese to combat B-26 Invaders during the Korean War. The La-11s in the Seoul raid wore DPRK-AF markings but were probably flown by Chinese pilots.)

The Korean War ended on 27 July 1953.

The summary above is not an exhaustive list of every Bedcheck Charlie raid, many more (usually single Po-2s) attacked frontline positions at night in ad hoc operations. Equally frustrating to the Americans was false alarms; as any engine noise in the distance at night might trigger an air raid alarm waking everybody up.

American responses

The first night fighter assets the United States had in the war were F-82G Twin Mustangs.

Contrary to popular lore, the F-82 Twin Mustang was not two stock P-51s mated with a center wing. There were dimensional differences, a revised vertical stabilizer, and a different electrical layout. None the less the F-82 did obviously descend from the P-51. Development started in October 1943 as a B-29 Superfortress escort which could fly 2,000 NM. The XP-82 prototype flew in June 1945, 2½ months before WWII ended. A production contract was immediately placed but none saw WWII combat.

The F-82G version was a night fighter version of low production in 1949. It was only intended to bridge the gap between the retirement of the last WWII P-61 Black Widows in 1950 and new radar-equipped jet fighters becoming available. It had a SCR-720C18 radar in a huge pod under the center wing.

Japan-based F-82Gs flew the very first American mission of the war (a reconnaissance flight to confirm South Korea was being invaded) and on 27 June 1950 also the first nighttime victory of the war, a North Korean La-7, a WWII-vintage fighter of Soviet origin.

Ironically, given its design and capabilities, most Twin Mustang operations in the Korean War were ground attack missions. Especially at the war’s start and then again when the Chinese army entered the war in October, every possible asset was needed for ground attack. The Twin Mustang was also hampered by an inadequate spare parts pool. F-82Gs departed the war in 1951. They did not shoot down any Bedcheck Charlies.

Another WWII fighter, the F7F-3N Tigercat, did. During WWII it was intended for the then-upcoming Midway class aircraft carriers. This twin-engine fighter was one of the most remarkable aircraft of the propeller era. The F7F Tigercat had a top speed of 400 kts and a 1,000 NM range. The prototype flew in November 1943 and production began in late 1944, but due to extended teething issues none were ever operational aboard US Navy aircraft carriers during WWII. A Marine Corps squadron ashore on Okinawa went active just prior to V-J Day but saw no action. After WWII ended Grumman’s Tigercat contract was significantly cut back.

(F7F-3N Tigercat at Wonsan, South Korea.)

The F7F-3N version was a two-seat model with a AN/APS-6 radar in the nose. As part of the US Marine Corps VMF(N)-513 “Flying Nightmares” unit, they deployed ashore to South Korea. Tigercats shot down two Bedcheck Charlies, both being Po-2 biplanes, one on 30 June 1951 and another on 23 September 1951.

One thing noted by Tigercat crews was the unexpected difficulty in using a high-performance fighter against the slow biplanes. The same had already been commented on by the B-26 Invader which shot down the first Po-2. The Tigercat crews estimated that their wood & fabric prey were flying at 60 kts, a -560% airspeed differential. It was hard to line up a firing pass as the biplane was, from the Tigercat’s perspective, basically a static point in the sky. This issue was especially acute for the sleek, streamlined Tigercat which had little drag to slow the plane as the engines were throttled back (during one intercept, the F7F-3N lowered its landing gear to bleed away enough airspeed). Care had to be taken not to slow under the plane’s stall speed (minimum forward motion to stay airborne) or run into the Po-2.

This would indeed be an issue for the the F-94 Starfire. This two-seat all-weather night fighter had been developed from the T-33 trainer which in turn was an offshoot of the F-80 Shooting Star fighter; which as the P-80 had been the first American jet to reach squadron service during WWII.

(F-94B Starfire at Suwon airbase during the Korean War.)

The F-94B version used during the Korean War was 44’6″ long with a 42’5″ wingspan. It was powered by an Allison J33 turbojet and had a top speed of 560 kts. In the nose was a AN/APG-33 air-to-air radar, which found targets for the four .50cal machine guns underneath. These night fighters first appeared in the Korean War during December 1951 but not in unit strength until March 1952. They did shoot down a number of planes (including three MiG-15 jets) at night, but not any of the Bedcheck Charlies.

One issue was that the USA feared the AN/APG-33 falling into the wrong hands and forbade Starfires from venturing too deep over enemy-held territory, less one be shot down and the wreckage recovered. This was not lifted until the final half-year of the Korean War.

A bigger problem was the airspeed differential issue, which was even greater than the propeller-powered Tigercat. Starfire pilots were trained to use the radar to line up an attack and the speed differential, compounded by the Bedcheck Charlies getting lost in the radar’s ground clutter, made this very difficult.

During February 1952, a F-94 was directed towards a Bedcheck Charlie by ground radar. The Starfire found the Po-2 and made three attempts at lining up a firing pass which were unsuccessful due to the biplane being so much slower than the jet. On the fourth attempt, the F-94 and Po-2 collided mid-air at 1,900′, destroying both.

In the same time frame, a F-94 trying to engage a Po-2 slowed beneath its own stall speed and crashed. A different Starfire trying to engage a Po-2 missed colliding with it by just 50′, according to the pilot. Following these three incidents the US Air Force prohibited Starfires from going below 2,000′ or 150 kts, even if it meant letting the Bedcheck Charlie get away. Combined with the restriction on not flying deep above enemy-held territory, this meant that the F-94 could not achieve what would seem on paper to be a trivial task.

Of all the tasks American airpower needed to accomplish during the Korean War, night air combat was only one and even of that one, dealing with the Bedcheck Charlie nuisance was only one of many nighttime jobs and probably the least urgent. None the less, despite the relatively small damage they usually caused, Bedcheck Charlies were an aggravation to exhausted soldiers and an embarrassment to senior commanders in that there seemed to be no effective counter.

In early 1951, one idea was to pair a big WWII-era plane like the C-47 Skytrain with one or more T-6 Texans. The Texan had been the best trainer in all of WWII and now during the Korean War was being used as a FAC (Forward Air Controller) and artillery spotter. The idea was that the big type would loiter dropping a “daisy chain” of para-flares, illuminating a broad swath of sky for the armed T-6 to hunt lone slow intruders. After deliberation, this idea was rejected as impractical. (As a side note, it was tried anyways later in the war with Corsairs instead of Texans, with limited success.)

As an experiment during June 1951, several US Navy F4U-4N Corsairs of USS Princeton (CV-37)’s air wing were dispatched ashore as “Detachment Dog” to “K-6” near Pyongt’aek. These were not strictly to fight the Bedcheck Charlies (there was also notable Chinese and North Korean nighttime missions of a more traditional character), but it was one of the tasks in mind.

(F4U-4N Corsair in South Korea.)

The F4U-4N version of the legendary Corsair had entered service late during WWII. It had a water-alcohol injection system for the engine which boosted horsepower, and a AN/APS-6 radar in a blister on the right wing. This radar had a maximum range of 4 miles.

(AN/APS-6 display. An airplane was represented by “twin blips”, the left one showing its range ahead of the Corsair and the right one its relative altitude difference. On the left image, a plane is to the left and below the Corsair. In the center image, it is level with the Corsair and dead-ahead. In the right image, the Corsair has closed range to the target. The “necklace” was interference from the ocean’s surface; over land this was more severe and irregular.)

The deployment of the nighttime Corsairs ashore was successful, and the F4U-4N version was joined by the F4U-5N and -5NL versions. These had been developed after WWII ended, and were the ultimate night fighter variants.

The F4U-5N had every possible improvement. AN/APS-6 was replaced by AN/APS-19 which had much increased range (10 NM which by modern standards, is still very short). Armed with four 20mm guns, it also retained all the underwing ordnance options.

(AN/APS-19 and four air-to-ground rockets under the right wing’s two 20mm guns.)

The night fighter versions of the Corsair were tremendously successful during the Korean War, performing every imaginable nighttime combat type. Against the Bedcheck Charlies, they were the most successful type: fast but not too fast, extremely maneuverable, reliable, and carrying a good punch with the 20mm guns so that one pass was usually enough.

the grass strip denial mission

Parallel to finding ways to shoot down the annoying harassment raiders, the USA also ran a second effort to stop the raids from happening in the first place.

During 1951, the United States began to target any suitable strip of grass by which the biplanes could operate at night. When it was announced, the plan must have seemed insane. The communist-held area was roughly the size and terrain of Kentucky. The biplanes needed only a flat grassy area about 150 yards long.

But from this, military cartographers deducted areas outside the Po-2’s range, then any with obstructions like ditches or boulders, and then any with tall trees at either end. Even the crude “Mule”s needed fuel and ordnance which came by truck, so any field inaccessible on the ground could be further discounted. Still, after all this, there were hundreds if not a thousand or more.

In what probably seemed like a hopeless endeavor, the plan was put into action. During daylight in mid-to-late 1951, F-80 Shooting Star jets dropped half-ton bombs on the empty fields. While it was relatively simple to just fill the craters back in, this would take at least a little time at each location. The US Air Force added 12-hour delay fuzes to some of the bombs to complicate this. At night when it was safer for propeller planes to operate, B-26 Invaders and F4U Corsairs conducted similar raids. These raids dovetailed into the larger and much more important overall “night interdiction” plan. The Chinese and North Koreans made most highway and railroad resupply runs at night, and the USA sought to hunt down and eliminate these.

(Under project “Redbird”, some B-26s in Korea were retrofitted with the AN/AAS-1 infrared “eye” in the nose. Developed by Bell Telephone, this early night-vision system required the WWII plane’s nose to be packed with dry ice to keep it cool. The AN/AAS-1 was useful for detecting heat signatures of blacked-out Chinese locomotives from a distance.)

The results of this effort can not be objectively quantified, as it is impossible to prove a negative (Bedcheck Charlie raids which never happened). By the time of the 1953 armistice, there was a notion that it was at least starting to bear fruit, if at least stopping the Bedcheck Charlie annoyances from increasing.

the supposed “stealth biplane”

In popular depictions of the Korean War, it is sometimes said that the Po-2 was “invisible to radars” and hence hard to defeat. This contains a glimmer of truth but is for the most part false.

Radar reflectivity is a complex equation based on many things. Naturally the size of the object and the distance from the radar are important.

Another important thing is faceting, which is to say, how much of the object faces the radar square-on vs how much of it is at an angle or rounded away. On this account the “Mule” surely is not a good choice, with all its supporting wires, fixed landing gear, propeller, and so on.

(Tail profile of a Po-2 “Mule”.)

Compared to sheet metal, fabric (and to a lesser degree wood) is a poorer reflector of radar. An amount of each radar pulse’s electromagnetic energy “gets trapped” in the tiny open spaces within the material, reflecting minutely less back. As the Po-2 was almost entirely fabric stretched over wood framework, it is provable and true that it reflects less back. The difference is however, negligible in most settings.

The main reason the North Koreans were able to sneak these planes in is more due to the technology level of American radars during the Korean War. Many of the ground-based radars dated back to WWII. These first-generation radars performed much better against planes at medium and high altitudes.

(WWII-vintage AN/TPS-1 at Yonpo during the winter of 1950 -1951.)

The AN/TPS-1 was a successful WWII ground radar which served again in the Korean War. During WWII, twin-engine bombers between 5,000′ – 20,000′ could be detected as far as 50 miles away. But if the target’s altitude was 1,000′ this was reduced by 50%+ and for single-engine planes even worse. The difficulties in Korea were compounded by the peninsula’s geography, which had many hills and valleys causing ground clutter which masked very low-flying aircraft.

Another problem is that the Po-2 flew so sluggish compared to the types radarmen were used to seeing, the operator might initially mentally ignore a Po-2 contact moving imperceptibly slow across his display.

There is no evidence that the Po-2’s construction had any real effect on American radars. To the contrary, there is ample evidence that the real issues were the ones listed above. For example during the last Bedcheck Charlie raid on Seoul in 1953, the strike package had the wood / fabric Po-2 biplanes, the mixed-material Yak-18 monoplanes, and the all-metal La-11 fighters. None of these were detected until all were nearly over the target, so it would not appear that any type of “magical biplane stealth” was in play.

totals during the war

The number of Bedcheck Charlie flights during the Korean War is unknown. Many of them were just solitary Po-2s causing no damage to nothing in particular, but waking people up. Many went unrecorded except in the memories of the GIs awakened. Conversely some of the recorded raids probably never even happened, and were called away when an airplane was heard in the distance at night.

Eight Po-2 “Mules” were confirmed air-to-air shootdowns during the war: one by a B-26 Invader, one by a F3D-2 Skyknight, one by a A-1 Skyraider, two by F7F Tigercats, and three by F4U Corsairs. A ninth was destroyed in the midair collision with the F-94 Starfire as described earlier. A tenth was hit by a F-94 and last seen trailing flames headed north, where the Starfire was prohibited to operate. As the Po-2 was made of wood and fabric, it is doubtful that one made it home, but per US Air Force regulations it was not counted. Another three Po-2s were claimed as hit by groundfire but none of these were confirmed.

Three Yak-18 “Max”s were shot down at night, all by F4U Corsairs.

One Ki-9 “Spruce” was claimed as downed by AA guns but not confirmed. More of these were destroyed on the ground.

The Tu-2 “Bat” is hard to quantify; while nine were shot down during the war (not all at night) there was no way if they had been sent on a meaningless harassment raid or on a regular, de jure nighttime bombing mission.

None of the MBR-2bis “Mote”s were shot down. Despite being the most intriguing of the types used, almost nothing is known of their operations along the northeast Korean coastline, other than they sometimes appeared at night dropping a few light bombs.

in popular culture

In the half-century since the Korean War, the Bedcheck Charlie phenomenon has been blown out of proportion in every regard: the number of missions flown, any tangible results they produced other than waking people up, and the severity which the United States put uopn the issue.

The American TV show M*A*S*H had an episode called “Five O’clock High” which dealt with this topic. It originally aired 22 September 1973. The plot centered on a hapless North Korean pilot flying a rickety WWII plane, trying to hand-bomb an ammo dump and repeatedly failing miserably.

To get a flyable, FAA-licensed, Soviet-made airplane in the 1970s United States was not an easy thing so the show’s producers instead substituted a PT-22 Recruit. During WWII, this had been a US Army introductory trainer. The PT-22, which was by then owned by a private pilot, was repainted in North Korean markings and looked suitably clumsy.

The topic overall continues to be of interest to military historians in the 21st century.

(Digital artwork of a Bedcheck Charlie mission.)