This rather odd-looking item is a wheelspanner. Ships' engineers and all submariners will be familiar with wheelspanners, as they are extremely useful for turning stubborn or jammed valve control wheels. (Think oversized garden faucet outlets.)
This particular one is somewhat unique. It is chromed--most were workaday hard steel tools. Also, the non-spanner end is shaped into a coarse screwdriver, perfect for screwing down deck fittings on an O-class submarine.
Each of the officers in the commissioning crew of HMC Submarine Okanagan was presented with one of these handy keepsakes by Her Majesty's Dockyard Chatham in 1968. Mine is on a shelf in front of me as I write, a constant reminder of those long-gone days.