Destruction of HMS Bulwark
On 27 November 1914, while taking on ammunition at Sheerness, she “suddenly blew up with an appalling explosion” (Official History vol.
II). When the smoke cleared the ship had entirely disappeared, along with all but 12 of her 750 crew. The scale of this explosion inevitably led to rumours of foul play, coming in a period of acute paranoia about German agents in Britain, but in mid-December a court of inquiry established that the cause of the explosion was an accidental ignition of ammunition. As would be demonstrated at Jutland, even the most powerful battleships were effectively floating bombs. Any spark on the long route between the quayside and the ship’s magazines could be fatal, bypassing all of the precautions to prevent such an explosion during battle.
The naval inquiry attributes apparent failures in the cordite storage procedures permitted by the officers responsible for the gunnery department aboard the ship for the disaster itself. Interestingly, one of the nearby boats from HMS Agamemnon reported seeing the periscope of a submarine, but the officers carrying out the investigation decided to ignore that bit of evidence as "improbable". It's interesting to consider the fact that periscopes were reported to have been seen at the sinking of both Britannic and Burdigala in the Kea Channel, so it makes you realise just how questionable some of these eye-witness accounts can sometimes be.