To put it simply, if the task here were a search of a ships hull, blowing up a mine or assaulting a beach at night there would be nobody better than the navy divers because that is what they are trained for, equipped for, and do regularly. Heavy lifting in deep water is clearly not their forte(which is no reflection on them). Commercial divers carry out multiple heavy lifts from deep water, per shift in all sorts of weather and tides. Its what they do day in, day out. Its their bread and butter. In fact they wouldn't even consider this a 'heavy' lift. Yes the navy will figure it out and probably achieve it but nowhere near as quickly or efficiently as the guys who do this type of task daily. Its not about North Sea vs Atlantic, military vs civilian, big boys waves vs little boys waves or anything else, its about using the correct tool for the job. As langball correctly pointed out, when a saturation diving bell is lowered to the seabed there is a 'heave compensation' system to mitigate against swell. Yes sat divers are somewhat subject to the effects of tide but nowhere near what a surface diver is. In 40 meters of water the surface diver has 40 meters plus of umbilical chord out, with the tide acting on the full length of it which acts like a parachute dragging him off the job and making work impossible. The saturation diver only has the distance from the bell to the job of umbilical out which might only be a few meters. The vessel can be moved to orientate the bell relative to the work so that his umbilical is in line with the tide if need be so he isn't getting dragged off. Crucially though, Diving from the surface with no decompression gives the navy divers only 10 minutes from the time they leave surface to the time they leave bottom. By the time they get to job, orientate themselves and figure out whats what, they must leave almost immediately. It is considerably more dangerous and difficult. Saturation divers can stay on the job indefinitely and even go back to the bell for a rest if they get tired. Surface diving is far more weather and tide sensitive for multiple reasons. There is a reason commercial divers and DSV's are used to recover downed helicopters in the UK. And there is a reason almost all work with any degree of technicality, carried out deeper than about 16 meters is done using saturation. As pumaboy said time is of the essence here.