The M15 class comprised fourteen monitors of the Royal Navy, all built and launched during 1915.
HMS M21
BL 9.2-inch Mk I – VII naval gun
The BL 9.2-inch Mk I–VII guns were a family of early British heavy breechloading naval and coast defence guns in service from 1881 to the end of World War I. They were originally designed to use the old gunpowder propellants.
Mk VI gun on disappearing mounting at Ben Buckler Gun Battery, Sydney
Training drill, 1890s
Forward gun on HMS Australia, 1893
HMS Iron Duke, a Mk III* or Mk VI gun in action at Maricourt, Battle of the Somme, September 1916