 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.Launched on 24 June 1915, she was completed in July 1915.