Until the 1970s, a very common method to dispose of unneeded munitions was to simply tip them off the side of a ship. This means that everything from grenades to chemical weapons have been languishing in large quantities around Europe’s shorelines, right alongside other types of unexploded ordnance (UXO).
This is a companion discussion topic for the original entry at https://hackaday.com/2024/06/28/cleaning-up-world-war-2s-legacy-on-the-seafloor-with-robots/