The process of canning food was invented long before a method of opening the cans was invented. Canning was invented by 1795 by Nicholas Appert, a Frenchman working to win the 12,000 franc prize offered by Napoleon for a method of preserving food for use by the army. The military secret was later spread as a food technology to England and the rest of the world. The instructions for opening a can were to basically use whatever you had to get it open, whether a hammer and chisel, knife, axe, shovel, rock, or whatever. Englishman Robert Yeates invented a can opener in 1855, #1577 (can someone get a jpg of a figure from that patent?), and this one was a version patented in the U.S. in 1870. Some familiar pocket or field can openers are at p-38, and P-38.