Submersibles may or may not carry crew, but the relative merits of crewing such craft are still debated. An uncrewed submersible is easier to construct – it does not have a life support system. The only problem is to make the vessel sufficiently strong to withstand the pressures found at great depths in the sea.
Using an uncrewed submersible also has many advantages to those involved in the work. Because the vessel does not have to come up for air, there is no time limit to the mission. The controlling crew can be changed on the surface and the work can progress with little disruption. Potentially hazardous environments and materials can be tackled with little worry. Finally, with only one crew, there can be no arguments about operational decisions.
However, uncrewed submersibles are not without disadvantages. It is much easier to lose equipment under remote control. Economies of construction often mean that uncrewed submersibles are reduced to simple structures which are prone to snagging in cables and other submerged obstructions. Many surface controllers find that because of the intense concentration demanded of them – not least because of the problems of interpreting a three-dimensional scene on a two-dimensional monitor – they can operate submersibles for only two or three hours. In fact, vision problems are probably the greatest argument against the use of uncrewed vessels of this type. Without the detail and the dimensionality of on-the-spot vision, many potentially disastrous and expensive decisions can be made by the surface controllers.
In the 1970s the complex demands of offshore drilling accelerated the development of crewed submersibles, and work in the British North Sea oil fields has brought about some of the most complex undersea technology. Generally, however, the trend is to develop uncrewed vessels. Advances in optical and other sensory technology, which are beginning to solve the vision problems, point toward fully automated (robot) submersibles in the future.