You've probably heard the expression that 'worse things happen at sea'. Sailor Robert Bruce wanted to make certain that these unspecified terrible things didn't happen to him when he was an engineer the Merchant Navy in the 1940s, so he carried this leather cosh and swichblade knife with him. Apparently he never needed to use them, but - to trot out another cliche - better to be safe than sorry, I suppose. The cosh and knife were donated to the Maritime Museum by his son Gary and are now on display in the Life at Sea gallery.
According to curator of port history, Ian Murphy, sailors were paid at the end of their voyage, sometimes getting several months back pay at once. This made them targets for all sorts of unsavoury types once they were ashore, so sailors felt most at risk in port. However, the tensions created by crews being shut up together for long periods and the presence of weapons on board, meant that many incidents actually happened aboard ship.