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I've heard from many WWII aviation hobbyists and WWII vets that the P-51 was essentially the pinnacle of U.S. piston-engine fighter design; it was fast, maneuverable, long-range, well-armed, allowed superb pilot visibility, etc etc.

So, why did the Navy never adopt it? It seems there were flight tests of the P-51D as a carrier fighter, modified with a tailhook for wire capture landings, but the Navy never pulled the trigger (so to speak). What were the primary reasons behind this decision?

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    $\begingroup$ The P-15, like many other fighters/pursuit planes, started off not well liked. It's performance wasn't very good either. Only evolutionary improvements to the airframe and a re-engining with a more powerful engine allowed the P-51 to reach its full potential. $\endgroup$ – Jim2B Jul 17 '16 at 4:37
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The biggest driver behind the use of the P-51 Mustang in naval operations was the need for B-29 escorts while bombing Japan. No naval fighter at the time had the range to accompany the B-29's so the P-51D was selected to determine if it could be a suitable carrier operator.

The test project was named "Project Seahorse", and one aircraft was selected and specially modified to cope with carrier landings.

enter image description here Navy Concept Image in Livery (Image Source)

The modifications included:

  • "Fin Fillet Extension" which enhanced low-speed operation.
  • Tail hook (for obvious reasons)
  • Catapult hook
  • High pressure tires
  • Higher pressure in the shock absorbers
  • Reinforced airframe

The modified P-51D started testing in September of 1944 under test pilot Robert Elder. The tests were carried out at Mustin Field in Phillidelphia on a modified runway fitted with a catapult and arresting cables. Throughout September 1944 to October 1944, 150 launches and recoveries were made on this modified runway. One big concern was that the aircraft would need to land around 90mph and the stall speed was 82mph, not much of a margin.

In late October 1944 the next stage of testing started, carrier landings/launches at sea. Lt. Elder made all the carrier landings at 85mph and was pleased with its handling characteristics, but there were issues:

  • Stall speed margin was extremely low, too low for safety
  • Rudder control at low speed and high angles of attack was inadequate
  • Landing attitude had to be very carefully controlled to avoid airframe damage
  • Go-arounds required slow throttle advancement. The extreme power of the Packard/Merlin engine meant that a high-power fast throttle advancement could put the aircraft into a roll or snap-roll. At low speeds this would prove a fatal mistake.

Only 25 launches/recoveries were made in the suitability trials and Lt. Elder did not believe that the Mustang had a place in carrier operations.

It was a moot point anyway. By early 1945 Okinawa and Iwo Jima were won by the allied forces. Each island had airfields that were taken over and provided a close base of operations for aerial attacks on Japan. In August 1945 Japan announced its surrender and it was official September 2, 1945. The P-51 wasn't required to be used from a naval platform anymore.

The project wasn't forgotten though. North American presented the NAA-133 based on the P-51H, which was a carrier operations "Mustang". It didn't go any further than the design stage though. In 1947 a P-51H was acquired to test new catapult equipment. Either way the war was over by that time and we didn't have to put any more effort into modifying the aircraft for carrier operations.

Here is my main source

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    $\begingroup$ Nice history lesson. $\endgroup$ – Robert Harvey Jul 15 '16 at 16:37
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    $\begingroup$ I didn't even know that I cared about this, but read the whole thing. Thank you! $\endgroup$ – user9394 Jul 15 '16 at 19:00
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    $\begingroup$ @Shane Lt. Elder is a test pilot. He's comfortable doing things on the edge and he probably felt comfortable getting it on the deck, but surely realized that the (above average) skills of a newly minted fighter pilot behind the controls of a 1200hp engine with wings would probably have difficulty in getting it on the deck without damage to them, the aircraft, other aircraft, and the carrier itself. $\endgroup$ – Ron Beyer Jul 15 '16 at 19:05
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    $\begingroup$ @Shane: There's no contradiction. What he "felt" when he flew the airplane pleased him - it was controllable and behaved well. However, when he realized that he was landing at 85mph he did not believe the aircraft was suitable because if he were to fly just 3mph slower the aircraft would not behave well and would most likely stall and crash. 3mph is enough for a gust of wind to cause a crash. Obviously, since he didn't die in a crash on that test he never "felt" the unpleasant behavior when flying the plane. $\endgroup$ – slebetman Jul 16 '16 at 2:33
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    $\begingroup$ As a side note, they also tested a B25/PBJ (in navy parlance) at the same time. $\endgroup$ – Davidw Jul 16 '16 at 8:26
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The P-51D's power-loading was more or less identical to that of the F6F-5; about 7.70 lb / hp at MTOW; the F6F was considerably heavier but had 30% more engine power with the R2800-1OW capable over 2,000 hp. The F4U-1 had a marginally lower loading being about a half-ton lighter than the F6F.

So it wasn't a case that the P-51D would have been too much for for Navy pilots on account of 'extreme power', though with a lower frontal cross-section and laminar-flow wings its acceleration may have been higher. The stalling speed would appear to have been the critical factor, largely as a result of the P-51D having a wing-area much smaller than either naval fighter.

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  • $\begingroup$ Would the engine type have been another consideration? All other American carrier-based aircraft were air-cooled engines which could take some amount of damage and continue to produce power; the Mustang's Merlin was liquid cooled making it somewhat less tolerant to damage. Under similar conditions, a Mustang's engine could be disabled, forcing a ditching where a Corsair might be able to power its way back to its home carrier. $\endgroup$ – Anthony X Jul 18 '16 at 1:02
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    $\begingroup$ The flying Tigers used a few P51 successfully against various Japanese aircraft including Zeros so fear of a Zero crippling the P51 was not an issue and the P51 had already shown superiority before the US entered WWII. P38, P39, and P51 where used side by side as B25 escort on Attu (Alaska) against the Japanese invasion but for some reason the P38 was the favorite in that campaign (perhaps twin engine or the nose gear had an advantage in the very rainy mud). $\endgroup$ – jwzumwalt Jan 2 '18 at 7:42
  • $\begingroup$ @jwzumwalt the extreme range and twin engines made the P-38 more suitable for the long distance fighter patrols and sweeps into Japanese held territory than other types. Having to fly for hours over open water without anywhere to make an emergency landing if you have an engine problem makes you appreciate having 2 of the things. $\endgroup$ – jwenting Jul 12 '18 at 5:22
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The Navy did not want the complexity of the liquid cooled engine and the need to supply and store coolant. AND the coolant is FLAMMABLE another problem the Navy did not want. The liquid cooled engines were also more susceptible to battle damage. The radials were a lot tougher in this regard and would make it back with damage that would stop the liquid cooled engines. When overflying a trackless ocean the Merlin would have increased the number of pilots lost. So far as the range thing. There were P51s and long range P47Ns flying missions to Japan from Iwo so the B29s had cover for daylight raids.

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  • $\begingroup$ ...they were operating carriers filled to the brim with bombs and avgas and they were worried about flammable radiator fluid? Sounds like someone needs to get their priorities straight... $\endgroup$ – Sean Jun 11 '18 at 16:06
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    $\begingroup$ @Sean not so much the flammability as the requirements for yet more consumables to be stored in already cramped ships. And more spare parts as the liquid cooled engines were more complex, requiring more and different spare parts as well. $\endgroup$ – jwenting Jul 12 '18 at 5:24
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The US Navy didn't need the P51 because they had the F4U Corsair, which had comparable performance, was better suited to ground attack work, and was designed from the start with a tougher structure suitable for carrier operation.

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Not mentioned above is a key design criterion that changes everything:

A carrier can sail to the area of action. An airbase cannot.

Longer range is always a good thing, as the Zero demonstrated. But in a general sense, carrier aircraft don't want to be hyper-optimized for range in the same way that one would have to for a land-based plane. So for a land-based plane you optimize for weight and aerodynamics, and if that means you have a wicked stall, fragile landing gear and 1/2 mile takeoff run, well, so be it.

And so you get the P-51. By any measure it was relatively light, especially compared to its Navy counterparts. And some models, like the H, were lightened even more. These were not going to last long on carrier ops!

The P-51's wing was selected specifically for low drag, even though it was known the design gave it high landing speeds and wicked stalls. Who cares? Just extend the runway a little and all will be fine. Again, not an option for carriers.

And finally, since you have lots of airbases, you don't really need to design your planes for multiple missions. So the idea of putting an easily-hit radiator full of boiling-hot caustic fluid on the bottom where it's easy to hit and directly under the pilot? Well, don't fly low. Again, the Navy doesn't have the luxury of space, you planes need to be able to survive all sorts of missions.

And this is why pretty much every attempt to make a carrier plane out of one originally designed for land use is doomed. Look, for instance, at the F-111B compared to the F-14A. Or one can read about the struggles of the Seafire.

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The P51 was not designed as a carrier aircraft. More specifically:

The airframe was not designed with a tail hook in mind. Putting a tail hook on a P51 airframe and then subjecting it to the stresses of a carrier landing would probably have pulled the tail off.

It doesn't have folding wings. Would have taken up a lot of room on a carrier deck and below deck, limiting spotting, and limiting the number of aircraft that could be launched within a given time frame. Being able to launch a large number of aircraft in a short period was a huge advantage, especially if an enemy raid is incoming.

The landing gear would not be rugged enough to handle carrier landings. To bring it up to that standard would necessitate both heavier gear and a heavier wing spar to take the stress.

The water cooled engine was not suitable for carrier operations. Heavier, and one lucky bullet meant the plane was going in the drink... and the pilot. The chances of rescuing a pilot whose location was unknown in the Pacific ocean were just about zero.

Aircraft design, even then, was a precise art, with tradeoffs to meet the desired goal. Changing the design later to meet a very different goal is likely to upset a lot of other design features. Simpler just to design a carrier aircraft from the ground up.

It is true that the Spitfire was redesigned for carrier operation as the Seafire, with decent results, but the British didn't have the resources to support a lot of different aircraft.

Note also that a dedicated carrier aircraft with performance in the general vicinity of the P51 was already available: the F4U Corsair.

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The Corsair was a good plane but was used more for ground operations. If anything made the Mustang unnecessary for the Navy it was the F6F Hellcat which replaced the Wildcat as the Navy's mainstay for carrier operations. The Hellcats performance in the Pacific was incredible (4,947 of 6477 enemy planes shot down) and was praised by many pilots. By the time the evolution of the Mustangs would have been good enough for the Navy they already had the Hellcat which started being used in 1943.

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