This is an iron cannon, dating from around 1750, which was one of ten cannon installed on His Majesty's Barque 'Endeavour', commanded by Lieutenant James Cook.
This asset is an artefact from Cook's first great voyage of discovery between 1768 and 1771, when he charted the east coast of Australia, claiming it for the British Government as 'New South Wales'.
It is evidence of the practice, common at the time, of lightening ships when necessary by jettisoning surplus weight - it was one of six canon tossed overboard in 1770 by order of Cook to help lighten the ship and float it off the hazardous Great Barrier Reef, where it had run aground.
It is evidence that Cook did not return to retrieve the cannon - it was not retrieved until 200 years later, when it was cleaned and conserved as part of a project funded by the Australian Government and presented to New Zealand for the commemoration of the bicentenary of Cook's visit to New Zealand in 1970.