dsc01218c.jpg

Detail of the firing end of the Vikers 4-inch submarine gun.

Google doesn't seem to think that there's any such thing as a "Vikers" gun, instead suggesting "Vickers" (although there doesn't seem to be any information about Vickers Mark IX 4-inch gun, either). The closest thing that Google suggested for "Mark IX gun" was the BL 4-inch Mk IX naval gun, but that doesn't really look like this gun, there's no mention of it being a submarine gun, and it wasn't introduced until 1917.