An apparatus having a bouyancy control tank mounted in conjunction with a submergible chamber, and being provided with a source of gas under pressure to the tank and wherein several vertically disposed pipes are arranged and constructed within the tank so that each pipe may be selectively opened from within the manned chamber for fluid communication from the tank to the ambient water below the tank. Pressurized gas to the tank forces water therein through a selected open pipe to the ambient water, so that a gas-water interface in said tank is attained at about the top free end of the opened pipe. To discharge gas under pressure from the tank, valves are mounted on the tank and which may be actuated from within the manned chamber or remotely, and with the discharge of the gas, water from outside the tank passes through the selected open pipe into the tank. The chamber is designed to provide a life-supporting environment so that bouyancy control operations may be conducted from within the chamber. This bouyancy control apparatus is particularly useful in limited diameter chambers and diving bells to attain positive bouyancy from any altitude for emergency ascent.