Submarines, submersibles and atmospheric diving suits usually operate at normal atmospheric pressure. It is a piece of diving equipment used by underwater divers, submarines and submersibles. Few unmanned submersibles are capable of descending to maximum hadal depths. This is acceptable for civilian research submersibles, but not military submarines. Also, a growing number of amateur submariners homebuild submersibles as a hobby. Rescue submersibles and parachute rescuers were deployed. An underwater telephone sometimes called Gertrude is also used to communicate with submersibles. His inventions include robots, trains, cars, flying devices, ships and submersibles among other things. The submersibles Mir 1 and Mir 2 carried the filming team on 12 dives. The Bathysphere itself served as a model for later submersibles such as the DSV Alvin. Some submersibles, such as bathyscaphes, dive and re-surface solely by controlling their buoyancy. The LTTE built several crudely built submersibles and semi-submersibles based on Narco-sub designs. Failure of submersibles under the immense pressure at hadal zone depths have occurred. Initial rescue efforts by "Pisces III" sister submersibles were unsuccessful. Filming in the deep ocean required the use of special submersibles.