The very cool-looking HMS X1, a British commerce raider submarine, the largest submarine in the world when she was launched in 1923.

She was designed as a "cruiser submarine", with two turrets containing two 5.2 inch guns on her upper deck. In theory, she would pop up, unload on a target, and then submerse to escape.

The turreted submarine cruiser concept was not very practical, so X1 was scrapped in 1936.