Holland 6 was originally a Holland-class submarine. But Holland 6 had many improvements made to her, and she was classed as the first of a class of 13 boats called the British A-class submarine.
See HMS A1 for details of her career in the Royal Navy.
References
edit- Hutchinson, Robert (2001). Jane's submarines : war beneath the waves from 1776 to the present day. London: HarperCollins. ISBN 978-0007105588..