What is a salt dog?

Salt dog or salt horse was the traditional term used in the Royal Navy and other navies for corned beef, and it appears in the literature from the beginning of the 18th century until recently. The term also appears in the United States Navy literature of the 19th century. As a consequence of the decline in sailing fleets, the name fell out of use in the 20th century, though the product, still called corned beef, continues to be issued by the British Ministry of Defence.