I have an interest in this and have followed the matter insofar as possible.
In WW II, some units were ordered not to carry pistols or big knives, lest they frighten civilians who might otherwise help a downed Allied pilot in Nazi-occupied country. This seems to have changed after D-Day, as the pilot might find his way back more readily to Allied troops. Some probably carried all along.
When Chuck Yeager was shot down and found his way across the Pyrenees into Spain, he had a .45 auto. I don't know if it was his or issued. His book didn't say.
Pilot in Asia seem to have been always armed, usually with .45 autos, or whatever they'd brought. Some photos show Flying Tigers with .38's, a Colt Official Police, in one good image. Those were privately owned. If you read, "Thirty Seconds Over Tokyo", Ted Lawson detailed his and his B-25 crew's sidearms: a mix of pistols, issued and private. He had his service .45 and his wife's Colt .32 auto. Many knives, but none named by make or model. I don't think he or his crew ever shot at anyone after crashing, but one gunner asked if he should fire on some Orientals approaching. They turned out to be Chinese, not Japs, and no shots were fired.
Korean arms were about what was used in WW II: .45's for USAF (plus what they owned, in some units, if not all. Navy and USMC still had Victory Models and a sprinkling of similar Colt .38's.
By the time the B-52 was in use, the Aircrewman .38's were adopted. It was thought that a very light gun was less likely to be ripped off the body as a pilot ejected. But I think they also liked the hi-tech image.
By the Viet war, the S&W M-15 was USAF standard, and both snubs and four-inch barrels were used. Some pilots supplied their own weapons, as unit shortages required it. I recall one pilot mentioning that in an account of his days in Vietnam.
Navy aircrew often used what they wanted. I think that author Stephen Coonts (A-6 Intruder pilot) had an S&W M-19 .357. A Navy helo crewman had a P-38, and mentioned it in his book on Walther's famous model. (Gene Gangarosa.) I personally saw Naval aircrew with Victory Model .38's in the 1960's. They were rumored to have S&W M-39 9mm's on some aircraft carriers.
A Naval pilot named Dieter Dengler hid his pistol on landing, but I forget if he named the sort. I recall thinking when I read his story that this seemed a defeatist thing to do. Many pilots are handgun-shy and never really get much training in what the pistol can do in the right hands.
When Scott O'Grady's F-16 went down over Bosnia, he complained that his Beretta M-9 was hard to keep free of rust. He also groused when his rescuers took the gun before they allowed him aboard the helo. I don't blame him! I hope that the gun was returned once they reached the aircraft carrier and his ID was confirmed.
I understand that some USAF units have bought Glock 19's with unit funds, but the M-9 is probably the most likely sidearm. I think Navy and Marine pilots get the SIG P-228 issued as the M-11. It is also issued to military investigators.
One thing it might be wise to avoid in a future war is carrying what the enemy does. A quite famous RAF pilot bummed a Luger from an intelligence officer, who had a cache of guns taken off of Luftwaffe personnel whose planes had crashed in Britain. I guess he felt it hit harder than the issue .38,which it does. Or, maybe he liked the "cool" factor.
All went well until his Mosquito was ambushed by a pair of FW-190's over Denmark and he and his navigator were shot down. The German troops who took his gun didn't look too happy about it, but didn't harm him.
Another very famous RAF officer carried a .32 Beretta. Don't know how he got it. Probably the same way that other fellow got the Luger. It was a pretty good choice, as it used ammo that could be found in Europe, and was small enough to conceal.
Because many US pilots wore shoulder holsters, it's hard to tell if they were armed. I'd like to see more photos showing the guns. RAF pilots often wore gray webbing belt holsters, and one can easily see the guns on them.
On Gunboards, someone posted a photo of a Webley WG .455 carried by famed Spitfire pilot Adolph "Sailor" Malan. He was South African, and the gun had been in his family since the Boer War. I guess he wore it for tradition or family pride. He may have just owned it. I'm not sure if it was the gun with him in his cockpit.
WW II Luftwaffe fighter pilots seem to have greatly preferred the Walther PP, as it was less bulky in their tight cockpits than the P-08 or P-38 holsters. I would be amazed if other .32's weren't used, some being private property. Hans Rudel, the Stuka pilot who was presented the Knight's Cross in gold, with swords and diamonds, wore a .25, but he didn't say which brand or model in his book.
I think that the top scoring ace of all time (352 kills!) carried a Walther .32. He was Erich Hartmann, and he refused to disarm when he went to receive the Knight's Cross or the swords or diamonds; I forget which. Those approaching Hitler were required to leave their pistols in an anteroom, but he said that he'd rather leave without the high award than take off his gun. Hitler was told, and allowed him to wear it. As one of Germany's greatest heroes, he had some "pull" that most wouldn't!
German bomber crews, especially enlisted men, usually carried the Luger. I don't think the Luftwaffe ever issued the P-38, by order of Goering, who preferred the older design. He had a financial interest in Kreighoff, who made Lugers, and was a gun enthusiast. If someone knows of Luftwaffe issue of P-38's, please speak up and cite your source. I'd be very interested. I think that panzergrenadier and paratroop units came under Luftwaffe control, for political reasons, and they may well have gotten P-38's.
That's about all that I know on the matter. Oh: the Italian Air Force and Navy used Beretta .32s, not the .380 issued by their Army. (Same basic pistol, but called the M-35, not M-34.)
The SIG- P-228 is probably as good a pilot's sidearm as I can think of, although it's kind of thick for concealed carry, if civilian clothes can be obtained after landing in enemy territory.
Under present conditions, I'd like to see the S&W M-66 again made and issued to aircrew. It is very versatile, and JHP ammo could be issued, as we are not now at war with a recognized nation. Full .357 ammo could be used for hunting and defense against animals. And many pilots prefer a revolver. (The reason has been discussed in this topic.)
It is likely that some pilots have had Ruger Speed -Six .38's, which have been issued to Army aircrew, as well as the S&W M-10. I think the Navy got some of both.
If someone knows more, please chime in! I'm especially interested in seeing WW II pilots' guns.
T-Star
P.S. I know the question pertained to fighter pilots' guns, but has everyone here heard about the B-17 waist gunner who shot down an ME-109 with a S&W .38? His .50 cal. was out of action and he drew the .38, which may have been a privately owned one. One of his bullets evidently got through the prop and killed the enemy pilot! It must have been the luckiest shot in history!
