HMS A1 was the Royal Navy's first British-designed submarine, and their first to suffer fatal casualties.
She was the lead ship of the first British A-class submarines (a second, much different A-class appeared towards the end of the Second World War), and the only one to have a single bow torpedo tube. She was actually sunk twice: first in 1904 when she became the first submarine casualty, with the loss of all hands; however, she was recovered, but sank again in 1911, this time when she was unmanned. The wreck was discovered in 1989 and is now a protected wreck
She was an enlarged and improved Holland class submarine - 40 ft (12 m) longer than the Royal Navy's five "Holland"-type boats. The most notable improvement was the addition of a conning tower. Subsequent A class boats were even larger and differed from her in several respects.
Like all members of her class, she was built at Vickers, Barrow-in-Furness. She was launched on 9 July 1902.