On 9 July 1917 HMS Vanguard – a dreadnought battleship – suffered a series of catastrophic explosions in Scapa Flow, Orkney. The ship and 843 men died. The enquiry concluded that an unintentional cordite explosion caused the loss of Vanguard, making this the biggest accidental loss of life in modern naval history.
The survey was self-funded and conducted by volunteer professional divers. Survey leader – Emily Turton – has made results available on line (Its a good read and well worth receiving)