There were 3 in the class, M1with a 12" gun as was standard for the class, also lost with all hands, M2 converted to seaplane carrier under post WW1 armament restrictions, and M3 converted to a mine layer and scrapped after the loss of M1 and M2.
An interesting story about M1, when it went on patrol it left its ceremonial gun tampions ashore in a chacon ( wooden storage container from CHatham CONtainer) a submariner from the time realised it was in the container and that no one would know of its presence, so took it, some 40 odd years later he had a fit of conscience and presented it to the Senior Rates mess of HMS Repulse ( SSBM submarines are capital ships and not referred to as submarines officially) The tampion was a work of art cast in bronze depicting a hippopotamus type creature with a large gun strapped to its back rising from the sea. I wonder where it went when Repulse decommissioned, has it been mislaid again? as far as I know it was never officially logged as an asset due to the previous keepers request to stay anonymous, in the RN, it doesn't exist if it has never been logged or listed as an asset