This is a German copy of the P38 can opener but far more heavy duty. These are post war surplus but I believe they actually debuted late in WWII though I am not 100% sure. I do know they can be difficult to get and are somewhat coveted among reenactors because they are so durable and pocket sized. It measures about 2 7/8" at its longest.
The price is for one. All are in overall good, usable condition, but a few do have some light rust and/or discoloration. They may still have a bit of grease on them.