A closed-loop rebreather, comprising a housing adapted to allow forward and backward passage of air during operation of the rebreather, a CO2 adsorbing canister contained within the housing, a counter lung extending from the housing, such that during rebreather operation, the air passes forward through the canister, into the counter lung and back through the housing, after which the air is recycled as forward passing air. The rebreather further including a bottle of compressed O2 operatively associated with the housing and adapted to continuously release O2 gas into the counter lung during rebreather operation.