Normally a submarine is a military vehicle and a submersible is a civil machine. The first seagoing submarine was built in 1879 by the Reverend Garett and was called the Resurgent. The first true submersible was probably the Turtle which was built in 1776 by a David Bushnalls. It was used by the Americans to attack the British Fleet in New York harbour. There were probably previous attempts before 1776 by people trying to make submersibles, but most of the activities prior to this date involved using upturned wooden or leather buckets, with compressed air being forced down to the divers by various mechanisms.


The first Royal Navy submarine was the Holland built in 1901 which carried 8 people. Today the present Trident submarines are 150M long, 3 times the height of Nelsons Column, and are powered by nuclear energy and have a displacement of 15000 tonnes. The Polaris submarines of the Royal Navy are somewhat smaller, but still displace 8500 tonnes and are capable of speeds of up to 30 knots. To propel a vehicle through the water at this speed takes tremendous energy. The typical electrical output of a Polaris submarine is sufficient to power a town.


Modern day submersibles are very special pieces of machinery, and those that go to extreme depths to explore the seabed where the Titanic lies are few in number. There are probably only 3 vehicles today that could reach such depths. ‘Alvin’ from Woods Hole Institute in the USA is one of them. There is also a French vehicle ‘Nautile’ and a Russian vehicle ‘Mir’ capable of descending the 2.5 miles to the Titanic.


A large portion of underwater exploration and inspection today is carried out by ROVs (Remote Operation Vehicle). These devices help overcome many of the problems which restrict human activity below the sea. Although these vehicles are very expensive and do get lost occasionally, their use is a safer approach than sending divers in to do the same jobs, by avoiding the increased human vulnerability and minimizing risk. Submarines and Submersibles often combine the ability to perform tasks underwater as ROVs and shelter humans from many of the conditions faced by divers, allowing humans to explore their underwater subjects in proximity and in safety.


Gemini is a recreational vehicle and has a depth range of 50M. Even at this depth the pressure on the hatches is about 14 tonnes, and the total pressure on the pressure vessel itself is about 125 tonnes. It has all the components of a large submersible, namely – surface buoyancy tanks, trim tanks, lead trim, lead acid batteries, life support systems, front and rear hydroplanes, a rudder and a very sophisticated control system consisting of a PLC (Programmable Logic Controller) and many electrically operated solenoid valves, pneumatic actuators, stepper motors, encoders and several electrical power systems. Its forward speed is 4-6 knots and when the surface buoyancy tanks are fully blown, it has a freeboard of 300-400mm. The design and control of the submersible combines just about every engineering discipline i.e. structural, electrical, mechanical, life support, physics, hydrodynamics and naval architecture.


Aquarius is Subeo’s production submersible, details and specification can be viewed on this site.