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The sign accompanying the Vickers 4-inch submarine gun. It reads

Vikers[sic] 4-inch Bore
Submarine Gun
WWI (1914)

The French-language portion of the sign notes that it's also known as a Vickers Mark IX 100mm gun.

Google doesn't seem to think that there's any such thing as a "Vikers" gun, instead suggesting "Vickers." Similarly, I was unable to find any information about a Vickers Mark IX 4-inch gun (the Internet seems to think that the Mark IX was a 12-inch gun).