Located half a mile off-shore between Tulsta Head and Cellar Head.
Operation Cauldron was a series of biological weapons tests (UK Biological Weapons Program 57) involving the spraying and bombing of pneumonic plague bacilli and brucellosis on a series of floating pontoons in September 1952
During the trials 3,492 guinea pigs and 83 monkeys were used in this manner. Humans as well as other animals ended up being exposed in these trials. On the last day of Cauldron, a fishing vessel, the Carella, strayed into the path of a trial using the plague. It ignored warnings to steer clear and unwittingly sailed through a cloud The trawler was tailed by two naval vessels for 21 days, waiting for any distress call causing concern about a possible plague outbreak around its home port in north-west England.
When none came, almost all records of the incident were burnt.
The crew of the Carella were unaware of the incident until approached by a BBC documentary crew more than fifty years later