In 1918, the Royal Navy suffered the loss of two submarines, with another three damaged along with a light cruiser. And you’ve probably never heard of it. It’s okay, I hadn’t heard of it either, and the British government went to great lengths to conceal the incident, because no enemy vessels were involved:
An underwater war grave containing the victims of one of the worst British naval disasters of the first world war has been surveyed for the first time so it can be preserved in the middle of a windfarm.
The two K Class submarines were destroyed on 31 January 1918 during the so-called battle of the Isle of May, in which 270 lives were lost. The two submarines were sunk and three more damaged along with a surface cruiser.
But no enemy ships were involved in the sinkings, 20 miles off Fife Ness on Scotland’s east coast. The deaths were all caused by a series of night-time collisions within the British fleet.
So embarrassing was the incident that even though one officer was court-martialed, the facts were not generally admitted for more than 60 years, until after the death of the last survivor.
A longer account of the accident is on the Wikipedia page. It’s pretty grim reading.
