Conducting a deep dive with a chest or sidemount rebreather using “Dilout” ( a combination of off-board diluent and bailout) has become more common with the advent of compact rebreather platforms. But there are issues to be considered. Here shipwreck enthusiast Justin Judd, details his and team mate’s gas planning approach for their recent CHO2optima dives on the HMS Britannic laying at a depth of 122m/400 feet.