The rusting Comet Tank (in service with the British Army 1949 to 1958) - it was obviously used as a bombing target for the RAF on Saltfleetby dunes.
Quite a walk to get to, especially from the 1st car park we went to, we turned back after walking about half a mile in thick gloopy mud and drove to another car park that Google Maps said was nearer. Carole stayed in the car as I walked the mile and bit to where it was in the mud flats, surrounded by tidal streams. Feet suitably soaked as I walked around her (I shall take my drone next time as I think it would give some great fresh perspective)