The Admiralty provided general specifications, but each shipyard did their own detailed design so that ships often varied in size.

The ships displaced 778 long tons (790 t) at deep load and their crew numbered 70 officers and ratings.

[3] The primary armament of the ships consisted of a pair of BL 4-inch (102 mm) Mk VIII guns in single, unprotected pivot mounts fore and aft of the superstructure.

The captain of Hydra was held liable for the collision because, although the other ship showed him a light, he did not perceive that it was on a crossing course.

[11] On 9 February 1921, Hydra collided with the Royal Navy torpedo boat Z 3 in the Weilingen Channel and sank.