Captured equipment can be very much of a mixed blessing if you’re trying to actually use it on the battlefield, especially big complicated pieces of equipment like tanks which are notorious for requiring a lot of maintenance and spare parts. Supplying spare parts to your own guys for your own tanks is already enough of a challenge; it can be downright impossible if your captured enemy tanks use components which aren’t an exact match for what your own factories produce. Ditto for ammunition: I don’t know if the Germans had 45mm guns on any of their tanks, but if they didn’t I can see why they would have replaced the KV’s 45mm gun with a flamethrower. When the French battleship Richelieu switched to the Free French side in 1943, and went to New York for a refit, the shipyard workers – whose experience and measuring tools and (literally) nuts and bolts were based on the imperial system of weights and measures – had all sorts of headaches working on the vessel, which had been built using the metric system. Sometimes the best use for captured equipment is study rather than combat, a good example being the T-34, which gave the Germans a considerable shock when they they saw the shells from their Panzers bouncing off of it. Once they had recovered from their embarrassment (among other things, at discovering that the supposedly backward Russians had successfully produced a diesel engine powerful enough for a tank, something which Germany had failed to do), they created their own version of the T-34, the Panther. Another good example is the Akutan Zero, an A6M Zero which crashed in the Aleutians during the diversionary operation for the Battle of Midway. The pilot was killed, and from the air the plane looked like it had been totalled, but in fact it was barely damaged. U.S. forces found it about a month later. It was dismantled, shipped to the States, reassembled, then throughly evaluated by test pilots. This told American pilots, and American aircraft designers, everything the needed to know about the Zeros’s strengths and weaknesses.