A pair of swivel canon mounted whaling grenade harpoon ends or tips dating to around 1950.
The tip to the left of the image is identical to the one described below and measures 35cm high.
Grenade harpoons  could reliably kill the biggest whales. At Coal Harbour’s ( Vancouver Island) museum there is a rusted, unarmed 1.5-meter harpoon, weighing about 60 kilograms, (as shown in the last image above)  designed to be fired from a swivel-mounted cannon: long metal barbs on the tip spring open after entering the whale, triggering an internal explosion that embeds the head deep into the body. A single shot was usually lethal.
The tip on the right measures 43cm.
Priced at £300 for the pair.