The O 9-class submarines were designed by J.J. van der Struyff, at the time chief engineer of the Royal Netherlands Navy (RNN).

[10] In addition to the torpedo tubes, each submarine had a single 8.8 cm cannon and a machine gun, which could be used against planes.

[8] The O 9-class submarines were equipped with two 6 cylinder two-stroke diesel engines made by the company Sulzer in Winterthur.

[4] This gave a capacity of 4350 Ah and allowed the submarine to operate solely on electric power for 3 hours.

[13] However, while leaving the harbor of Den Helder the O 11 got rammed by the surveillance vessel BV 3 and as a result of severe damage sunk.