Submarine Warfare Insignia

The Submarine Warfare Insignia (usually known as "dolphins" or "fish") are worn by qualified submariners.

In the Royal Australian Navy Submarine Service, sailors who qualify as submariners are awarded a badge depicting two dolphins and a crown. This badge (known as a sailor's 'dolphins') was designed by Commander Alan McIntosh RAN, and was introduced in 1966.

The British Royal Navy Submarine Service first issued badges to crew members during the 1950s, and adopted the current badge depicting two dolphins and a crowned anchor in 1972. The "dolphin" is a second specialization earned after completing initial training in a chosen trade.

The French Navy has three levels of badges:

The first two can be worn by officers or enlisted.

Enlisted Sailors and Naval Officers wear a dolphinsuniform breast pin to indicate that they are qualified in submarines. The Submarines insignia is considered one of the Navy's three major enlisted warfare pins, along with the Surface Warfare Badge and the Enlisted Aviation Warfare Specialist insignia. To earn the right to wear "fish", prospective submariners complete an extensive qualification process that lasts about one year (for both enlisted and officers, though the two programs differ significantly) and covers virtually all of the submarine's systems. Once an enlisted sailor has earned the right to wear the "dolphins", (SS) is added after his rate of rank that stands for "Submarine Specialist".

On 13 June 1923, Captain Ernest J. King, Commander, Submarine Division Three (later Fleet Admiral and Commander in Chief, U.S. Fleet, during World War II), suggested to the Secretary of the Navy (Bureau of Navigation) that a distinguishing device for qualified submariners be adopted. He submitted a pen-and-ink sketch of his own showing a shield mounted on the beam ends of a submarine, with dolphins forward of, and abaft, the conning tower. The suggestion was strongly endorsed by Commander Submarine Division Atlantic.

...
Wikipedia