The military use of divers in warfare was, until 1918, largely restricted to the salvage of damaged ships, clearing of channels blocked by wrecks, and assorted ships’ husbandry duties. One significant clandestine operation conducted during the First World War was the recovery of code books and minefield charts from a sunken German submarine. This was of more significance as an intelligence operation, although the diving activity was also kept secret.
During the First World War, Italy developed a human torpedo or chariot that was used in 1918 to attack an Austrian battleship in Pola Harbour in what is now Croatia. The attack was a success in that the ship was sunk, but, unfortunately, it coincided with the fall of the Austro-Hungarian Empire, and the ship was already in friendly hands! The potential of this method of attack was noted by the Italian Navy. They put it to use in the Second World War with divers wearing oxygen rebreathing sets as underwater pilots. In passing, it is interesting to note that the idea of the chariot was suggested to the British Admiralty in 1909, and Davis took out patents on a small submarine and human torpedo controlled by divers in 1914. This was pre-dated by a one-person submarine designed by J.P. Holland in 1875.
Diving played a greater part in offensive operations during the Second World War. Exploits of note include those of the Italian Navy. They used divers riding modified torpedoes to attack ships in Gibraltar and Alexandria. After a series of unsuccessful attempts with loss of life, they succeeded in sinking several ships in Gibraltar harbour in mid-1941. Later that year, three teams managed to enter Alexandria harbour and damage two battleships and a tanker. Even Sir Winston Churchill, who did not often praise his enemies, said they showed ‘extraordinary courage and ingenuity’. Churchill had previously been responsible for rejecting suggestions that the Royal Navy use similar weapons.
In Gibraltar, a special type of underwater war evolved. The Italians had a secret base in neutral Spain, only 10 kilometres away, and launched several attacks that were opposed by British divers who tried to remove the Italian mines before they exploded.
Divers from the allied nations made several successful attacks on enemy ships, but their most important offensive roles were in the field of reconnaissance and beach clearance. In most operations, the divers worked from submarines or small boats. They first surveyed the approaches to several potential landing sites. After a choice had been made, they cleared the obstructions that could impede the landing craft. One of the more famous exploits of an American diving group was to land unofficially and leave a ‘Welcome’ sign on the beach to greet the US Marines, spearheading the invasion of Guam. The British Clearance Divers and the US Navy Sea, Air, Land Teams (SEALs) evolved from these groups. The Clearance Divers get their name from their work in clearing mines and other obstructions, a role they repeated during and after the Gulf War.
The research back-up to these exploits was largely devoted to improvement of equipment and the investigation of the nature and onset of oxygen toxicity (Chapter 17). This work was important because most of these offensive operations were conducted by divers wearing oxygen breathing apparatus. The subjects were the unsung heroes of the work. This group of scientists, sailors and conscientious objectors deliberately and repeatedly suffered oxygen toxicity in attempts to understand the condition.
Oxygen-nitrogen mixtures were first used for diving by the Royal Navy in conjunction with a standard diving rig. This approach was based on an idea proposed by Sir Leonard Hill and developed by Siebe Gorman and Co. Ltd. The advantage of this equipment is that, by increasing the ratio of oxygen to nitrogen in the breathing gas, one can reduce or eliminate decompression requirements. It is normally used with equipment in which most of the gas is breathed again after the carbon dioxide has been removed. This allows reduction of the total gas volume required by the diver.
During the Second World War, this idea was adapted to a self-contained semi-closed rebreathing apparatus that was first used extensively by divers clearing mines. This development was conducted by the British Admiralty Experimental Diving Unit in conjunction with Siebe Gorman and Co. Ltd. The change to a self-contained set was needed to reduce the number of people at risk from accidental explosions in mine-clearing operations. The reduction, or elimination, of decompression time was desirable in increasing the diver’s chances of survival if something went wrong. The equipment was constructed from non-magnetic materials to reduce the likelihood of activating magnetic mines and was silent during operation for work on acoustically triggered mines.