Good afternoon. Well, this is the less "vehicle" gun of the series! BL 12 inch Mk, 47 tons in yoke mount, as seen in one of the Portsmouth Solent Forts.
First armed with 12.5 inch RML guns, from 1884 the artillery was replaced with BL guns, and due the restricted space, they used the yoke mount. Protected by armor (I think that it was iron, not steel), concrete and granite from the seaside, theese forts were very impressive. Cheers.