<P> Food preserved in tin cans was in use by the Dutch Navy from at least 1772 . Before 1800, there was already a small industry of canned salmon in the Netherlands . Freshly caught salmon were cleaned, boiled in brine, smoked and placed in tin - plated iron boxes . This canned salmon was known outside the Netherlands, and in 1797 a British company supplied one of their clients with 13 cans . Preservation of food in tin cans was patented by Peter Durand in 1810 . The patent was acquired in 1812 by Bryan Donkin, who would later set up the world's first canning factory in London in 1813 . By 1820, canned food was a recognized article in Britain and France and by 1822 in the United States . The first cans were robust containers, which weighed more than the food they contained and required ingenuity to open, using whatever tools available . The instruction on those cans read "Cut round the top near the outer edge with a chisel and hammer ." The gap of decades between the invention of the can and can opener may be attributed to the functionality of existing tools versus the cost and effort of a new tool . </P> <P> Dedicated can openers appeared in the 1850s and were of a primitive claw - shaped or "lever - type" design . In 1855, Robert Yeates, a cutlery and surgical instrument maker of Trafalgar Place West, Hackney Road, Middlesex, UK, devised the first claw - ended can opener with a hand - operated tool that haggled its way around the top of metal cans . </P> <P> In 1858, another lever - type opener of a more complex shape was patented in the United States by Ezra Warner of Waterbury, Connecticut . It consisted of a sharp sickle, which was pushed into the can and sawed around its edge . A guard kept the sickle from penetrating too far into the can . The opener consisted of several parts which could be replaced if worn out, especially the sickle . This opener was adopted by the United States Army during the American Civil War (1861--1865); however, its unprotected knife - like sickle was too dangerous for domestic use . A home - use opener named the "Bull's head opener" was designed in 1865 and was supplied with cans of pickled beef named "Bully beef". The opener was made of cast iron and had a very similar construction to the Yeates opener, but featured a more artistic shape and was the first move towards improving the look of the can opener . The bull - headed design was produced until the 1930s and was also offered with a fish - head shape . </P> <P> The first rotating wheel can opener was patented in July 1870 by William Lyman of Meriden, Connecticut and produced by the firm Baumgarten in the 1890s . The can was to be pierced in its center with the sharp metal rod of the opener . Then, the length of the lever had to be adjusted to fit the can size, and the lever fixed with the wingnut . The top of the can was cut by pressing the cutting wheel into the can near the edge and rotating it along the can's rim . </P>

What class of lever is a tin opener