USS Mackerel (SS-204), the lead ship of her class of submarines, was the first ship of the United States Navy named for the mackerel. Mackerel and her near-sister Marlin were prototype small submarines which the Navy was exploring to replace the aging S-class submarines.

The Mackerel-class submarines were a pair of experimental prototype submarines built just prior to World War II and launched in 1940 and 1941. The two submarines were similar in size and capability to the S-class submarines built at the end of World War I, and had been ordered to test the feasibility of using mass production techniques to build small submarines. Until at least 1940 it was thought that mass production of fleet submarines would be impractical, and in any case small submarines could provide area defense for submarine bases. Once it became apparent that there would be sufficient production of the more capable Gato-class submarines, interest in the design waned and no additional small submarines were ordered. Submarine production standardized during the war on the Gato class and its successors, the Balao and Tench-class submarines. In some references, the Mackerels are called the "M class".