[1] Periscope
[2] Pressurized conning tower, housing devices for navigation and maneuvering in surface and immersion
[3] Torpedo launching tube
[4] Trimming tank
[5] Tank for flooding the torpedo launching tubes
[6] Tank for compensating the weight of torpedoes
[7] Electric motor, used for navigation in immersion
[8] Diesel engine, used for navigation in surface
[9] Regulation tank
[10] Maneuver room
[11] Batteries for feeding the electric motors
[12] Fresh water tank
[13] Tank for compensating the weight of torpedoes
[14] Trimming tank
[15] Torpedo launching tube
The above illustration depicts one of the first attack submarines deployed in action by the German Imperial Navy during the First World War.