Hi, Geoff,

Most of the older wwI wwII subs had saddle-tanks. These were outside the pressure hull, and open at the bottom. On top were the Kingston Valves, usually operated by compressed air, but with a system that allowed them to be operated by hand as well. On submerging, the valves would be opened, allowing air to escape through them, and once the boat had reached a certain depth (for some it was periscope depth), they were closed again. To surface, compressed air was blown into the tanks, displacing the seawater and making the sub buoyant again.

Kingston Valves, or their modern counterparts, are still used on some vessels, particularly Diesel-Electric boats.

Hope that helps, no drawings, unfortunately,

Garth