The J class of submarines was a seven submarine class

Ship class

A ship class is a group of ships of a similar design. This is distinct from a ship-type, which might reflect a similarity of tonnage or intended use. For example, the is a nuclear aircraft carrier of the Nimitz class....

 developed by the Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 prior to the First World War in response to claims that Germany was developing submarines that were fast enough to operate alongside surface fleets. Six were completed during mid-1916, while a seventh entered service at the end of 1917.

Although larger and more powerful than previous British submarines, the J class could not keep up with surface vessels, and operated independently during the war.