8th May 1952

Biological weapons tests begin in the Outer Hebrides

Government researchers arrived off the coast of Stornoway, Isle of Lewis, on 8 May 1952, ready to start experiments with a variety of infectious pathogens. Their samples included the bubonic plague – otherwise known as Black Death.

The experiments were part of Operation Cauldron, a series of biological weapons trials carried out in the early days of the cold war, much like the anthrax trials that had been conducted in 1942 at Gruinard Island.

Operation Couldron

The experiments were a significant undertaking, involving dozens of personnel working across a research vessel called Ben Lomond, and a 61- by 18m pontoon. The pontoon was designed to sit low in the water and able to tilt so the researchers could set it up to face into the prevailing wind.

Test animals, confined to cages, would be secured to the pontoon and the biological agents released, either by spraying them into the air, or detonating small bombs. The wind would then carry the agents to the test subjects so they would be naturally infected. Once they had been exposed, the animals were taken back to the Ben Lomond and kept under observation. Those that died were then autopsied to determine exactly what had killed them, and how.

Unintended consequences

Several hundred animals were subjected to the tests, including monkeys and guinea pigs. On average, three trials were conducted every day throughout the test period, with each one requiring around 225 guinea pigs.

Not everything went according to plan. Locals and boats in the area were told to stay away, but one fishing trawler called the Carella sailed directly through a cloud of plague. It was allowed to continue to sea but monitored by a warship to ensure nobody aboard showed signs of infection before coming back to land.