the last Mustangs in the US Army

The P-51 Mustang was one of WWII’s greatest fighters and one of the best era-adjusted fighter planes of all time. Within the American consciousness it is almost synonymous with WWII.

Decades after WWII and after the P-51 had left service as a fighter, the Mustang briefly “came back from the grave” to serve not in the US Air Force, but in the US Army.

(P-51 Mustang during WWII.)

(F-51D Mustang chase plane follows the Sikorsky YUH-60A prototype during the US Army’s UTTAS competition of 1976, seeking a replacement for the UH-1 Iroquois of Vietnam War fame. Sikorsky’s design defeated Boeing’s YUH-61 to win UTTAS and was developed into the UH-60 Blackhawk of today.) (official US Army photo)

(US Army F-51 Mustang during 1970s experiments with airborne recoilless rifles.)

the Mustang after WWII and the division of American airpower

The P-51 Mustang was a standard fighter in its class at the end of WWII in September 1945 and remained in service.

(P-51 Mustangs at Conn Barracks in the post-WWII American occupation zone of Germany. During WWII this was Flugplatz Schweinfurt of the Luftwaffe, home to a Ju-87 Stuka unit and later a fighter tactics school.) (photo by Peter Randall)

On 18 September 1947, the US Army Air Forces of WWII was split off into an independent fifth branch of the USA’s military, the US Air Force. One of the first changes was altering the aircraft nomenclature series, for example the pursuit (P-) category was rolled into a new overall fighter (F-) category and hence the P-51 Mustang became the F-51 Mustang.

For three days in March 1948, the heads of the armed forces met in Key West, FL to iron out what roles the air wings of the five armed forces would fill. The goal was to prevent inter-service squabbling or duplication of missions. It was agreed that the US Air Force would handle all strategic missions, land-based fighters, reconnaissance missions, ground attack duties, air logistics, and many other duties. It would also assist the US Navy with land-based overwater missions. The US Navy and by extension US Marine Corps would continue carrier-based aviation, shipboard helicopters, and land-based anti-submarine missions. The US Coast Guard’s tiny air wing was so specialized that it had already found its niche.

Finally this left the US Army. It would have a rump air wing, oriented towards “hyper-tactical” roles like the transport helicopters of air cavalry units, scout helicopters, little artillery spotting lightplanes, medevac helicopters, and a small number of utility planes.

This delineation of tasks was called “the Key West Agreement” and was made official Pentagon policy on 1 July 1948. It has remained so ever since.

(An example of US Army fixed-wing aviation after the Key West Agreement is this L-20 Beaver utility plane, here taking off from the WWII-veteran aircraft carrier USS Corregidor (CVU-58) during 1958.) (official US Navy photo)

As for the Mustangs in the US Air Force, by the start of the 1950s they were mostly in Air National Guard units, with the Korean War resulting in some being federalized and again returning to frontline combat service. After the Korean War surviving aircraft were transferred back to ANG units where they were soon replaced by jet fighters.

(“Wham Bam”,  a F-51D of the West Virginia Air National Guard, the very last Mustang in the US Air Force.)

The last Mustang user overall – at least until the chase planes described below – was the West Virginia ANG. On 27 January 1957, it retired its last F-51 Mustang. It was the last Mustang in the US Air Force and the last remaining propeller fighter of any type still in use.

chase planes

There in not much to elaborate about chase planes, as the concept is not complex. A chase plane follows another aircraft, usually a prototype or experimental design, on test flights as an observer. Chase planes are still used today in the 21st century but during aviation’s golden age, were even more important. Not until the 1950s did test flights have regular access to ground tracking radars, and inflight data recording and telemetry links came even later. If there was a crash, observations of the chase pilot were often the first step in determining what went wrong. They were also useful in real-time. For example if the test pilot reported severe turbulence but the chase pilot didn’t, it might indicate an impending problem on the aircraft rather than weather issues.

There is no rigid criteria for a chase plane. No air force is going to spend money developing a type just for this role, so they were invariably just some other existing design.

That said, there are a few loose needs. The chase plane has to have performance slightly superior to whatever it is chasing; obviously a chase plane slower and less maneuverable than the test aircraft would be of little use. At the same time it can’t be “too superior”; for example nobody would want a supersonic jet fighter as the chase plane for a prototype piston-engined trainer.

Other than that, there is little else needed for the job. During and after WWII, warplanes of the WWII generation were used as chase aircraft during test flights.

(P-40 Warhawk serving as the chase plane for the Douglas XB-19 over Los Angeles, CA during 1941.)

The P-40 Warhawk fighter served various Allied air forces during the first part of WWII. Only one XB-19 strategic bomber was built, as it was never ordered into production. The gigantic lone prototype served as a utility and test plane throughout WWII and then a year afterwards. The XB-19 was bigger than any production WWII bomber and the United States would not try a bomber this large again until the B-36 Peacemaker of the early Cold War era.

(P-51 Mustang serving as the chase plane for the second XP-82 prototype.)

Contrary to popular lore, the F-82 Twin Mustang was not two stock P-51s joined at the factory by a center wing section. It had a different electrical system, different tail structure, and other alterations. None the less it was clearly derived from its single-seat cousin. The F-82 Twin Mustang did not see combat during WWII but fought in the Korean War.

(P-61 Black Widow serving as the chase plane for the XB-35 prototype during 1946.)

The P-61 Black Widow was a successful night fighter of WWII, serving on until 1950. Northrop’s XB-35 project started early in WWII however development was protracted and not completed until WWII’s end. By the time the prototype was ready for test flights during 1946, the peacetime military had limited interest in a new piston-engined bomber and no order was placed. The design was reconfigured for jet engines as the YB-49. That type also never entered service.

The United States had a lot of high-quality types in inventory after the end of WWII in 1945 so it might seem logical that they would appear as chase planes for a long time afterwards, but that was not the case. Aeronautics was moving at an incredible pace after WWII and the problem was simple: even the best WWII types were soon just too slow. For example the XP-86 prototype, which would become the F-86 Sabre of Korean War fame, first flew only 25 months after Japan surrendered and the prototype YB-47 Stratojet bomber only ten weeks behind it.

(The third prototype Vought X-F6U jet fighter at Naval Air Test Center Patuxent, MD preparing for a flight in 1948. Its chase plane, a WWII F6F Hellcat, is already airborne and waiting.)

Design of the F6U Pirate carrier-based jet fighter started in December 1944 but the US Navy did not realistically expect it to enter fleet service before WWII ended. Only 33 Pirates were built and they only served 3½ years. Technology was advancing very fast.

One WWII fighter could marginally keep up as a chase plane, but it was one which did not see any active combat during WWII. The P-80 Shooting Star was the first American jet fighter to enter mass production. During WWII a few were deployed to Europe but none saw active combat. Redesignated F-80 after 1947, these saw combat in Korea and also use as chase planes during the first decade or so after WWII.

(F-80 Shooting Star chase plane with the prototype Lockheed XF-90 during 1949.)

A F-80 Shooting Star served as the chase plane for the swept-wing XF-90 during the summer of 1949. The XF-90 was 52% faster than a F-51 Mustang, which was still in use as a fighter at the time. The XF-90 was not selected for service. Off-topic, the XF-90 prototype was used as a target for a 1950s nuclear weapons test in Nevada after the project’s cancellation. During 2003, the smashed-up plane was rediscovered in the desert. With a half-century having decayed the radioactivity, the wreckage was taken to the USAF Museum in Dayton, OH for display as an artifact of 1950s nuclear testing.

the Cheyenne and the Mustang

(AH-56 Cheyenne)

The story of how the WWII legend P-51 Mustang briefly came “back from the grave” as chase planes began in 1964 with the US Army’s Advanced Aerial Fire Support System competition for a dedicated attack helicopter. This in turn would later intertwine with the post-WWII Key West Agreement which had been struck when the Mustang was still in service as a fighter.

Previously after WWII the US Army had armed some transport helicopters with door guns, then starting in 1962 began to assign “gunship” transport helicopters with no troops aboard to escort air cavalry helicopters. The next step was a dedicated attack type dispensing with a passenger cabin altogether. In what was supposed to be an interim step only, the AH-1 Cobra was quickly designed and put into production, pending a proper winner of the AAFSS competition.

Lockheed’s submission was the Cheyenne. Somewhat out of the scope of this writing, the two-seat AH-56 was a remarkable aircraft, either now in the 2020s or certainly for 1967 when the first prototype flew. It was a compound helicopter, with a vertically-oriented pusher propeller on the extreme rear receiving up to 75% of the engine’s power in forward flight. Much of the lift was provided by 26’7″-span airplane-style wings.

The gunner, who sat in the forward position, had a seat which rotated in unison with either the nose 40mm grenade launcher or belly 30mm autocannon, so he was physically looking the same direction as the weapon’s muzzle. Six hardpoints allowed use of unguided rockets or BGM-71 TOW missiles; for the latter the Cheyenne had night vision and laser rangefinder, with the gunner using a helmet sight. The pilot had a primitive digital “waypoint” feature by which he could lock in a particular location, and then let the navigation system guide him there for an attack.

(A BGM-71 missile fired by the Cheyenne prototype against a target hulk WWII M4 Sherman tank. This is probably painful for military museum curators of the 21st century to see, but the military still had a lot of relic WWII hardware in the late 1960s / early 1970s.) (photo via Lockheed-Martin)

The Cheyenne flew 190 kts in normal flight with a top speed of 212 kts. For 1960s comparison, the top speed of a AH-1 Cobra was 149 kts while the top speed of the then-most common helicopter, the UH-1 Iroquois, was 109 kts.

How the WWII Mustang entered the equation was the need for something to serve as the chase aircraft. Previously when the US Army tested a new helicopter, it simply used another helicopter. Now this would be impossible; the Cheyenne was twice as fast as a Huey and would leave it in the dust.

At the same time, as mentioned earlier, a chase plane is best not “too” much faster, as (especially with helicopters) a large portion of the test flight program is not full-bore speed runs but rather handling crosswinds, transitions to and from hover, etc.

For these reasons the US Army took the unusual step of resurrecting a WWII fighter for chase plane duties more than two decades after WWII had ended. The US Army procured three previously demilitarized Mustangs: a (basically) “stock” F-51D and two Cavalier Mustangs.

the three aircraft

The first Mustang obtained by the US Army was originally a P-51D, serial # 44-72990, ordered under the 1944 budget and built in 1945. The D model was the most common Mustang of WWII, with 8,102 built or roughly half of all versions combined. After WWII this particular plane went to the Royal Canadian Air Force, which retired it in 1959. Sold as surplus to an American buyer, it was refurbished for recreational flying with guns removed and a second “rumble seat” in the cockpit. This plane was acquired commercially by the US Army in 1967 specifically as a chase plane for the AH-56.

(The basically “stock” F-51D after being acquired by the US Army in 1967. Behind it is a U-8 Seminole utility plane, and behind that a CH-47 Chinook helicopter.) (photo via mustangsmustangs.com website)

After receiving this F-51D, it was considered a success for the chase plane role and two more Mustangs were acquired in 1967 – 1968. These were Cavalier Mustangs which are described later below.

(The two Cavalier Mustangs acquired as Cheyenne chase planes.)

but why?

The Mustang was not the only type suitable for being a chase plane to the Cheyenne. For example the T-37 Tweet, a jet trainer of the era, had a flight envelope roughly the same as the WWII propeller fighter. It cruised at 310 kts and topped out at 369 kts and was a decently-maneuverable plane already in military service.

Why exactly the US Army took the unorthodox route of using a WWII fighter plane in 1967 has been lost to time, and it is possible there really wasn’t one single reason. The Mustangs, either the modified F-51D or the two Cavaliers, had a second seat for a photographer, were as fast and as maneuverable as the Cheyenne, had no safety issues, and were not a big-dollar procurement. All things being equal with more contemporary types, something had to be selected and the Mustang ended up being it.

Perhaps another factor, for the second and third Mustangs, was that this was during a high point of interest in the Cavalier aircraft company within the United States government.

Cavalier was originally Trans-Florida Aviation Inc., a company founded in 1957 as the last F-51s left Air National Guard service. CEO David Lindsay’s vision was that the glut of Mustang airframes being disposed of by the Pentagon could be converted into private use; specifically that business executives might buy them and use them both for recreation and business travel. Trans-Florida took surplus F-51s and gutted them, zeroing out the airframe fatigue life and rebuilding the engine. The WWII gunsight and other remaining combat features were removed. Plush leather seating was installed, and a passenger seat was installed behind the pilot. A luggage compartment was added. To keep pace with FAA regulations a new radio was installed as was a Regency civilian flight transponder. Two removable fuel tanks were mounted on the wingtips. The tail was replaced by a new design 1’2″ taller.

(A F-51 Mustang being “cavaliered” at Trans-Florida’s Sarasota, FL factory during October 1961.) (photo via swissmustangs.ch website)

Mr. Lindsay’s vision for the “Executive Mustang” never caught on and sales were very poor. The concept was rebranded as the “Cavalier Mustang”, oriented towards sports flying, with only a handful more being sold during the early 1960s.

Things looked to possibly be turning around in the late 1960s when the Department Of Defense became interested in Cavalier Mustangs. The US Air Force had no interest in them itself, however, it was considered a good idea for supporting small, third-world allied air arms. A lot of these small air forces were flying WWII-surplus warplanes into the end of the 1950s. Now for the 1960s counter-insurgency (COIN) strike role the USAF considered that to aid them, it might be less preferable to wean them onto low-performance jets and more preferable to just give them another (updated) WWII piston-engined type. The company had proven itself competent with a contract to overhaul the Dominican Republic air force’s F-51 Mustangs.

Trans-Florida renamed itself Cavalier Aircraft Corporation. Three versions were made available: the Cavalier F-51 which was a rebuilt P-51D airframe, the Cavalier Mustang II which was the same but with weapons restored, and the exotic Cavalier Mustang III which used a Rolls-Royce Dart turboprop engine.

The two planes selected by the US Army as chase aircraft were Cavalier F-51s, the simplest of the three types. The Department of Defense considered the Cavalier rebuild so extensive that they were deemed “new” airplanes reusing some old components, and as such, the two received new serial numbers of the fiscal year 1968 series; 21 years after actual P-51 production had ended.

the Cheyenne test program

The AH-56 evaluation had two phases. The first ran from the first flight in September 1967 until April 1969. During this phase, the Cheyenne clearly demonstrated itself as a remarkable helicopter but was also found deficient in several key areas, mainly the flight controls, empty weight, and pilot workload. The US Army issued a “cure notice” which cancelled Lockheed’s planned production contract but did not altogether cancel the AH-56, leaving it an open developmental contract.

Lockheed was still confident in the design and worked out the problems. Test flights resumed later in 1969.

(One of the Cavalier chase planes shortly after delivery in November 1968.)

The Mustangs, the F-51D and two Cavaliers, worked exceptionally well in their role as chase planes for the Cheyenne. During 1968, the US Army issued a new pilot’s manual for the F-51 tailored for the chase plane role. It will remain almost certainly the last American military manual for operating the Mustang.

Both the modified F-51D and the two Cavalier rebuilds performed equally well. Between the two, surprisingly the F-51D was considered a favorite if there was one, as it was regarded by ground mechanics as less demanding to maintain.

(The modified “stock” F-51D. Warplane serials of the time used the last two digits of the contract year as their first two numerals, with the first digit truncated off. During the early post-WWII years and Korean War era this was no problem as aviation was advancing so rapidly, it was rare for a plane to stay in service more than a decade. As some WWII-generation planes lingered past the mid-1950s longer than expected, this presented an issue as a serial number might be repeated every 10 years. A prefix “0-” was added, the humor being that the 0 was really an O meaning “Old”.)

(One of the two Cavaliers with a UH-1 Iroquois. Like the Mustang had been during WWII, the Huey is often associated as the “classical” Vietnam War aircraft.)

(One of the two Cavaliers with a CH-54 Tarhe behind it.)

The demise of the Cheyenne is outside the scope of this writing and even today remains a debated topic. The final round of test flights were during 1972. Only two deficiencies were noted, an issue with the rigid rotors stalling and mediocre performance in bad weather.

The Cheyenne’s biggest hurdles were not mechanical but rather political. Within the US Army, the AH-56’s abilities were of course strongly wanted but there was hesitation at the Cheyenne’s complexity. US Army field mechanics would be servicing something basically on the same technology tier as high-performance US Air Force aircraft. At the same time, the supposedly interim AH-1 Cobra performed very well in Vietnam.

An unrelated, and probably bigger, problem was a simmering dislike of the project within the US Air Force. Since the post-WWII Key West Agreement, there had previously been little inter-service squabbling between the US Air Force and the US Army.

During 1966 US Air Force Gen. J.P. McConnell and US Army Gen. Harold Johnson held an informal meeting, sort of a “20 years on…” follow-up to the Key West Agreement, to look at how airpower had evolved. It was agreed that if the US Army abandoned interest in regaining fixed-wing strike planes, the US Air Force would be fine with it flying armed helicopters.

However now the Cheyenne was such an unexpectedly advanced thing that the USAF began to have second thoughts. The Cheyenne seemed to intrude upon the “A-X” attack plane concept the USAF was seeking funding for. The US Air Force lobbied Congress that the US Army was encroaching on its ground attack mission and that the Cheyenne should be cancelled.

In 1972 the US Army started the Advanced Attack Helicopter competition for an eventual replacement for the AH-1 Cobra. A lot of the AAFSS competition’s criteria overlapped that of the new AAH competition, and that may have been intentional. At the same time the Pentagon added a two-engine criteria to AAH, eliminating the single-engine Cheyenne from “re-submission” into the new competition. Perhaps the final nail in the coffin was an estimate that production Cheyennes would cost $500,000 more than originally envisioned; giving the Department Of Defense a politically-friendly reason to end the project. The Cheyenne was permanently cancelled that year.

The Mustangs had proven themselves as good chase aircraft and remained in service after the Cheyenne’s cancellation.

(The US Army Aviation Engineering Flight Activity was located on the grounds of Edwards AFB, CA. This 1977 photo shows an interesting lineup, with the WWII Mustang sharing apron space with aircraft of the Vietnam War and early post-Vietnam eras.) (photo via ARC online forum)

(One of the later helicopters the Mustangs served as chase planes for was the Hughes YAH-64A prototype which eventually became the AH-64 Apache.)

By the late 1970s the US Army had obtained great service from this surprising choice of a chase plane, but was ready to move on. A pair of T-28 Trojans, a propeller trainer of the mid-Cold War era, replaced them. With one of the Cavaliers already detailed to the recoilless rifle trials described later below, the last to go was the modified “stock” F-51D.

(photo by Larry Kline)

This F-51D made its last US Army flight on 7 February 1978. It was sent for museum display to Ft. Rucker, AL. With that the P-51’s career with the US Army ended, 38 years after it had started and three decades after the US Army gave up fixed-wing combat planes.

(North American Aviation’s NA-73X private-design prototype which eventually became the P-51 Mustang.)

the recoilless rifle trials

One of the “chase Mustangs” had another quite interesting mission after the Cheyenne’s cancellation.

During the summer of 1974, the Department of the Navy (the US Navy and US Marine Corps) tested a concept for a low-cost air-to-ground weapon to arm FAC/TacRec (forward air controller / tactical reconnaissance) types, mainly the USMC’s OV-10 Bronco.

Warplanes like the Bronco normally “target-find” for artillery or airstrike assets, perform battlefield reconnaissance, etc. They are not really intended as strike planes in their own right, but based upon experiences during the Vietnam War the US Marine Corps considered that giving them a decent air-to-ground ability might be beneficial. “Targets of opportunity” like an enemy tank unit vulnerable in road transit could be immediately attacked while an airstrike or howitzer fire was made ready. The plane might also pick off isolated targets like a scouting armored car not worth its own strike package, or give emergency help to friendly infantry on the ground at risk of being overrun.

The problem was suitable ordnance. Free-fall bombs had significant effect but in the tiny numbers one Bronco might carry, were unlikely to score first-pass hits. Once dropped, they were gone. Unguided rocket pods had a better area effect, but were unlikely to disable or destroy the latest Soviet tanks. And again, once the pod was fired there would be no second chance. First generation smart bombs like the Bullpup and Maverick were in service but defeated the low-cost objective, or were too big, or both.

It was theorized that a recoilless rifle mounted on a plane might be best: these had the punch to knock out a tank, were decently accurate, and could be repeatedly fired. The USMC had previously considered their use to deliver “willy petes” (white phosphorus target-marking rounds) but now wanted to perhaps just use them as de jure weapons.

(The “flying artillery” concept was by no means novel or new in 1974. During WWII, Beech designed the XA-34 Grizzly. It was centered on a T15E1 75mm autocannon in the nose. Both the T15E1 and XA-34 were very successful, however the Grizzly shared components with the B-29 Superfortress which was a higher priority. When production bottlenecks finally ended, Japan was near defeat anyways and there was no interest in fielding yet another new warplane type. The XA-34 was cancelled.) (photo via Old Machine Press)

Leonardo da Vinci is often credited with the original idea for a recoilless rifle but the concept wasn’t fully perfected and mass-produced until WWII.

(US Army paratroopers engage German forces with a M18 during 1945. One of the earliest and smallest recoilless rifles, the 57mm M18 was designed for tripod use but was light enough to be fired like a traditional rifle as seen here.)

A recoilless rifle is not a bazooka-type rocket launcher, although it often fills the same tactical niche. A recoilless rifle is a true firearm with a chamber and rifled barrel, firing a gun-configuration cartridge (casing, propellant, bullet). The difference is that recoilless rifle rounds have a perforated casing, which expels combustion laterally into a bellmouth at the rear end of the gun, countering the force exerted on the departing shell going the other way and negating its felt recoil.

By this a relatively lightweight, man-portable weapon can fire ammunition of calibers equal to that of towed field artillery. The disadvantages are that the projectile’s range is significantly less, and that use produces a back-blast danger zone along with significant noise and smoke.

(The M344 round used by the Mustang during the 1974 experiments. It is actually 105mm but labeled “106mm” to avoid confusion with incompatible 105mm ammunition.)

After WWII recoilless rifles had been repeatedly considered, and rejected, as ordnance for warplanes.

(Harvey Aluminum Company designed a lightweight recoilless rifle which could be semi-automatically reloaded. It was not accepted for production.)

The most major stumbling block was that recoilless rifles are hand-loaded with the breech being in the extreme rear of the gun. Unlike a machine gun or autocannon, there was no practical way to do this remotely and automatically external to an aircraft. The solution developed was for an internal magazine in the center of the plane’s fuselage, feeding downwards. A hydraulic “shuttle” would strip a round out of the magazine, carry it above the gun on an arm trailing behind the breech, lower it and chamber it, then catch the bellmouth section swinging it upwards, putting the rifle into battery.

There were lesser problems with the concept, and these are what the F-51 Mustang aimed to explore. A recoilless rifle produces a significant backblast. It was unknown how this would affect airflow over the plane’s tail. A recoilless rifle’s round flies a relatively flat profile. As a weapon designed to be static-fired on the ground, it was unclear how it would perform when fired off an object already moving through three dimensions.

As the US Army had no further use for all three chase Mustangs by 1974, it loaned one of the Cavaliers to Naval Air Weapons Station China Lake, CA for US Marine Corps use. Watervliet Arsenal, NY provided two M40 105mm recoilless rifles and ammunition. The Mustang was flown by LtCol John Pipa of the US Marine Corps but remained painted in US Army colors.

For certain, there was zero interest in actually fielding this system on Mustangs. The Cavalier Mustang was just an available airframe. The M40s were mounted on the Mustang’s wingtips, replacing the Cavalier fuel tanks. The elaborate auto-loading system was not used, and the guns were hand-loaded on the ground for single-shot use.

During the spring of 1974, the idea was tested against two target hulk trucks in the desert. Firing took place with the WWII fighter in a 22º dive at 250 kts. The slant range to the trucks was 5,072yds or roughly a 2¾ miles line-of-sight for the pilot.

Mid-June, a final determining test series was run.

Out of eight shots from the Mustang, one direct hit on a truck was scored. The other seven rounds landed in a tight grouping. The US Marine Corps concluded that the marginal inaccuracy was likely due to flexing of the WWII wings on the Mustang, which would not be present on the rigid under-fuselage mounting envisioned for production use.

The pilot reported that the backblast of the M40s did not disrupt airflow around the tail and in fact, the only noticeable effect was the extremely loud noise produced by all recoilless rifles.

The concept was also investigated by mounting non-firing weapons on an OV-10 Bronco and a A-4 Skyhawk, plus a full firing set-up on a bizarre arrangement with a Bronco fuselage / cockpit section suspended from a gantry. That was as far as it went. Like a number of other early post-Vietnam War projects, Congress had no interest in funding it and the idea died.

The US Army did not want the test Cavalier Mustang back in 1974 and it was sold to a civilian owner.

postscript

In both the helicopter test flights and the gunnery test, the reborn Mustangs were an operational success and a budgetary one as well. The US Navy’s budget for the whole recoilless rifle project was $95,000 ($579,251 in 2023 money) which would have easily been exceeded by the flight-hour costs on a modern jet alone.

Somewhat off-topic, the head-butting between the US Army and US Air Force over the Cheyenne was the last of its type. When the AH-64 Apache helicopter and A-10 Thunderbolt II jet respectively entered use, both the US Army and US Air Force stated that overlaps between them were unavoidable and beneficial. In December 2022, the US Army picked Bell’s V-280 Valor winged tiltrotor as the replacement for the UH-60 and other helicopters, and again the US Air Force did not object. The Key West Agreement, struck 3 years after WWII, still seems to be good policy in the 21st century.

(photo by Larry Kline)

When the F-51D chase plane was retired in February 1978, perhaps there was a bit of silent satisfaction that the P-51 Mustang had ridden off into the sunset wearing US Army green, as it had when it began during WWII.

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