Deep sea diving has been around for thousands of years. The ancient Greeks practised commercial and military diving with little equipment except for a rope and a stone weight. Inventors in the 17th century sought ways of keeping divers submerged for longer. They supplied fresh air from a surface pipe, held up by a float, into the diver’s armoured suit.

In the early 19th century Auguste Siebe invented a more practical diving suit consisting of a helmet attached to a waterproof jacket. Air was pumped into the helmet through a surface pipe. However, this suit had open vents at the bottom to allow the air to escape, the water was held down by air pressure so, if the diver fell over, it would result in him probably drowning as water would pour in through the vents.

Siebe’s later suit was a closed type, a modified version of which is still in use today. It had the advantage of letting air out without letting water in, whatever the diver’s position.

In 1943 Jacques Cousteau and Emil Gagnan perfected their SCUBA (Self Contained Underwater Breathing Apparatus). Commercial, industrial and recreational divers now use this widely. The diver carries the units so they are free to move around as they wish. It consists of either an open circuit Aqualung or, a closed circuit re-breather where exhaled gas is recycled. Aqualungs are widely used in recreational dives because of the ease of use. The re-breathing unit is more complicated to use and requires more training however, it enables the diver to stay submerged longer as less oxygen is used, leads to less decompression problems and releases no air bubbles so is ideal for marine conservation and photography, or for covert work.

ADS (Atmospheric Diving Suits) can be used by individual divers to descend to great watery depths. An ADS resembles a suit of armour and allows movement of the limbs whilst maintaining the same internal pressure throughout. There is no need to decompress or have special gas mixtures, which makes it less dangerous as well as making diving simpler. With this equipment, divers can stay submerged for hours to depths of -700m/2300ft. Some ADS even contain their own propulsion units.

The deepest recorded dive by a skin diver, which is without special equipment, is a depth of -214m by Austrian Herbert Nitsch in 2007, earning him the soubriquet ‘the deepest man on earth’.

In 1960, the deepest manned dive in history occurred in the Mariana Trench, the deepest part of the world’s deepest ocean. A two-man submersible, the Trieste, containing the oceanographers Don Walsh and Jacques Piccard plumbed the staggering depths of -10915m/-35810ft and actually sat on the bottom of the most fathomless part of the earth. This depth has never again been attempted in a manned craft and possibly never will. They recorded sightings of never seen before marine creatures and fish proving that life does exist in this most unfavorable of places although the almost mythical giant squid eluded them.

Nowadays deep-sea submersibles such as the three-man Alvin regularly trawl the murky depths of the oceans. Since 1964 Alvin has made more than 3000 dives to an average depth of -1829m/-6000ft. It has two robotic arms and can be fitted with mission-specific sampling and experimental gear. It can dive for up to nine hours with one pilot and two scientists on board.