Pocket-sized and consists of a short metal blade that serves as a handle (which doubles as a flat-blade screwdriver), with a small, hinged metal tooth that folds out to pierce the can lid. A notch just under the hinge point keeps the opener hooked around the rim of the can as the device is "walked" around to cut the lid out. The tiny, lightweight, P-38 (38mm in length) collapsible can opener was developed during World War II, reported to have been a rapid 30 days design project in the summer of 1942 by the U.S. Army Subsistence Research Laboratory in Chicago, IL. The origin of the name is not clear. Some claim it required exactly 38 punctures around a can to open it. Others say it performed with the speed of a P-38 fighter plane. Whatever the case, it is clear this little device has to be considered one of the most perfect inventions ever designed for use in combat. The P-51 (51mm in length) is the big brother to the P-38 Can Opener. It was designed in the 1980s as the big brother to open #10 cans and the large 36 soldier meal pack or T-Packs. About twice the size of the P-38 but about twice as easy to use due to it's larger handle.