Intended as a shore bombardment vessel, M15s primary armament was a single 9.2-inch Mk X gun which had been held as a spare for the and s.[1] In addition to her 9.2-inch gun, she also possessed one 12-pounder and one six-pound anti-aircraft gun. She was equipped with triple expansion steam engines rated to 800hp that allowed a top speed of 11kn. The monitor's crew consisted of sixty-nine officers and ratings.
M15 was ordered in March 1915, as part of the War Emergency Programme of ship construction. She was laid down at the William Gray shipyard at Hartlepool in March 1915 and launched on 28 April 1915. The vessel was completed in June 1915.
M15 was towed to Malta in July 1915, where she received her main armament. She then proceeded to Mudros, and later was involved in the defence of the Suez Canal.
After bombarding Gaza as part of the Third Battle of Gaza, on 11 November 1917, M15 and the destroyer were torpedoed by the submarine . 26 men lost their lives in the sinking of M15, 1km (01miles) from shore, in of water.[2]
In 2020, Hamas divers recovered ammunition, including large-calibre naval shells, from the wreck of M15 with the intent of using explosives from the shells to make warheads and gunpowder propellant to make rocket fuel. After more than a century at the bottom of the sea,while Israeli sources claim the material was found to be unusable Hamas published a video of their members using it to make rockets .[3]