During and before World War II, various nations would collect information on foreign and enemy weapons, which would be printed in pamphlets.

The best example of this is the German Kennblatter fremdes Geräts, which contains a wealth of information on foreign equipment used. The practice of printing instructional booklets on enemy weapons was by no means exclusive to the Germans, for example, in 1941 the Russians had a manual titled "Как в бою воспользоваться трофейным оружием" (How to use captured weapons in battle) on the MG34. The manual is quite accurate, which is impressive given how the Germans invaded in June of the same year.

Now, as for the Americans and their foreign weapon manuals, I have not been able to find any documentation concerning the operation of anti-aircraft guns in specific. That is however not to say, that heavy weaponry was ignored entirely in these pamphlets. As in these pictures, the documentation did not shy away from going into detail with regards to the heavier weapons. It would surprise me if the know-how on how to operate German anti-aircraft guns was not available to the Americans. Indeed, the Flak 38 is listed in the following catalog of enemy ordnance

However, that is not say this is entirely realistic or probable. Anti-aircraft guns require a crew of multiple people to operate effectively. The Flak 38 in Call of Duty WWII is no different, and is operated by 5 men. Firing at 450 rounds per minute cyclic and having only a 20 round magazine, you can see it requires frequent magazine changes. Magazines themselves need to be reloaded. It goes without saying that a crew needs to be well trained.

So, I don't know the context of this game, but if a group of soldiers is tasked with capturing a Flak 38, they know beforehand what gun it is through some sort of reconnaissance conducted earlier, they familiarize themselves with the available documentation on the weapon, then yes, it's possible to operate the weapon, although not as effectively as a German crew, of course. There's also the issue of friendly units mistaking the German weapon for, well, a German weapon and crew. It's a situation that has friendly fire written all over it.

So I have to stress that it's a "yes" with a lot of ifs and buts.

Sources:

• Kennblatter fremdes Geräts Heft 1

• Как в бою воспользоваться трофейным оружием: MG34

• Linked album: Special Series No. 14, German Infantry Weapons, May 25, 1943, as prepared by the Military Intelligence Service of the War Department.

• Catalog of Enemy Ordnance