Operation Cauldron

Operation Cauldron was a series of secret biological warfare trials undertaken by the British government in 1952. Scientists from Porton Down and the Royal Navy were involved in releasing biological agents, including pneumonic and bubonic plague, brucellosis and tularaemia and testing the effects of the agents on caged monkeys and guinea pigs.

The experiments were carried out at sea, off the coast of the Isle of Lewis in the Outer Hebrides, aboard a floating pontoon, supported by the ship Ben Lomond. The test animals were placed in cages on the deck of the pontoon and biological agents dispersed either from a bomb suspended from a boom or by being sprayed. After being exposed, the animals were taken aboard the Ben Lomond and those that died were dissected to determine the cause of death. 3,492 guinea pigs and 83 monkeys were used in the tests.

The tests were initially judged to be a success, both in terms of the effectiveness of the biological agents and the test platform. However, a year later, this decision was reversed, with the tests on plague bacteria being described as a "failure" and the statement that "brucellosis has not increased its reputation as a dangerous agent."

In the final test of the series, the Fleetwood-based trawler Carella, with a crew of eighteen, ignored warnings to steer clear and unwittingly sailed through a cloud of plague bacteria (Yersinia pestis) on its return from a fishing trip to the waters around Iceland, causing concern about a possible plague outbreak around its home port in north-west England. The Carella was not stopped for disinfection or medical examination but was kept under covert observation by a destroyer and a fisheries vessel for twenty-one days, and the ship's radio communications were monitored for any kind of medical distress call. The surveillance period included a period of shore-leave at Blackpool, during which the crew mixed with the people of the town as usual. None of the crew became ill.

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