The availability of ten 6 inch Mk XII guns from the Queen Elizabeth-class battleships in 1915 prompted the Admiralty to order five scaled down versions of the M15-class monitors, which had been designed to utilise 9.2 inch guns.

HMS M31 and her sisters were ordered from Harland & Wolff, Belfast in March 1915.

In 1916, she defended the port city of Yanbo, in Saudi Arabia, against the Turkish army by providing artillery cover for the Arab rebels.

Equipped to carry 52 mines, she was renamed HMS Melpomene in December 1925.

She was renamed HMS Menelaus in 1941, and was finally sold in 1948 and broken up at Llanelly.