Excursion is a combined closed circuit oxygen / semi-closed circuit nitrox Tactical Diving Life Support System that provides an operational diving capability beyond the safe depth and time exposure limitations of oxygen.

To switch to the nitrox gas supply stored in a separate pressure vessel (cylinder), the diver rotates a multi-turn gas switch-over valve that provides a constant mass flow of nitrox gas into the breathing circuit. Following a gas switch from oxygen to nitrox, the diver may descend to a maximum depth of 24m using 60/40 nitrox or to 30m using 50/50 or 40/60 nitrox.