With a large, powerful fleet, the British navy had never considered underwater warfare important and consequently any bright ideas received little encouragement. The British Army, however, were keen to develop commando-style raids in enemy-occupied Europe and took great interest in the Italian small-craft assaults. During 1940 and 1941 British Intelligence in Spain reported a great deal of Italian activity on the Spanish mainland, and following the early Italian pig attacks on British shipping, an Italian submersible with breathing apparatus was recovered.

 

Interested in this underwater weapon, the army began developing a copy of the Italian submersible and initially sent sixteen members of the Royal Engineers, 21 101 Troop (Dover), to begin training at HMS Dolphin in the use of Davis Submarine Escape Apparatus: the most senior was Sergeant Don Craig.

The sinking of the battleships Queen Elizabeth and Valiant in Alexandria harbour substantially reduced the capabilities of the British Mediterranean fleet and attracted the attention of Prime Minister Winston Churchill.

Recognising the weapon’s potential for destroying the giant German battleships threatening his North Atlantic convoys, Winston Churchill wrote to General Ismay, Secretary to the Chiefs of Staff, on 18th January 1942.

Please report what is being done to emulate the exploits of the Italians in Alexandria harbour and similar methods of this kind. At the beginning of the war Colonel Jeffries had a number of bright ideas on this subject, which received very little encouragement. Is there any reason why we should be incapable of the same scientific aggressive action the Italians have shown? One would have thought we should have been in the lead. Please state the exact position.

With the Prime Minister involved, the human torpedo project came to the attention of the ambitious Flag Officer of Submarines, Sir Max Horton, KCB, DSO. He had begun his career at the bottom of the ladder but was soon in command of an M Class submarine during the First World War. He hated red tape and had the reputation for taking risks; he was a complete disciplinarian as well as being totally ruthless, removing all those who stood in his way. Sir Max Horton now wanted this high-profile project, arguing that any activity involving diving should come under his command and the Submarine Service, and he got his way.

On 24th January 1942 the order for the construction of six human torpedoes was placed with Messrs Stothert and Pitt, crane manufacturers. In their factory at Bath a corner was screened off with corrugated iron to maintain complete secrecy. Only the most trustworthy employees were selected to carry out the work, each one being sworn to secrecy, and only allowed into the restricted area with a special security pass.

Work began manufacturing the three sections that made up the cylindrical hull of the British human torpedo. The explosive warhead, the centre and the tail sections were constructed of 3/32 inch non-magnetic steel and then bolted together to form what appeared to be a large conventional submarine torpedo. The three sections of superstructure were then added to give the craft its unique appearance and all were constructed of wood, creating buoyancy to keep the machine upright when underwater. In front of the driver, who would be sitting astride in an upright position, were the instruments, behind a protective shield taller than that of the Italian machine because their men lay on the hull, crouched like jockeys.

In the centre, between the two divers, was the rectangular buoyancy tank, which was free-flooding. The valve on the top was opened to allow the air to escape while the water entered from the holes at the base of the tank, and the machine sank. At the rear was the boson’s locker, fixed to the hull by brass straps, and used to carry magnets, rope, and the net-lifting ram, which was subsequently replaced by net-cutters.

The bosun’s locker was free-flooding; the early models had holes cut into the sides, but the later ones had doors. The hull was painted olive green, but before final assembly the internal parts were fitted. Inside the tail section were the 2-hp (1.5-kW) electric motor, air bottles, air pump, drum controller and rear trimming tank. The centre section held thirty batteries arranged in two rows and the forward trimming tank.

At the very front was the detachable warhead, with 600 lb (272 kg) of high explosive in the centre compartment, and on either side a buoyancy compartment to which lead weights could be added to obtain neutral buoyancy to stop the warhead sinking or floating to the surface. The detonator was set from the outside by the diver turning the electric clock mechanism, which could be set for sixty-minute intervals up to ten settings.

Having produced the chariot, along with the diving suit and breathing apparatus, it was necessary for Admiral Horton to find a method of transportation that would deliver the men and their weapon close to an enemy harbour without being detected. A submarine was his obvious choice, but other extreme methods were considered, such as the conversion of a Halifax bomber that would drop men and machine by parachute. These operations were carried out under cover of darkness. Consequently, the possibility of man and machine being reunited seemed unlikely, and for this reason the hair-brained scheme never became reality.

On 9th March 1942, the director of Naval Air Division at the Admiralty convened a meeting to consider transporting chariots by aircraft or glider.

By June 1942 Admiral Max Horton had referred the matter to the Combined Operations Committee, who recommended the Catalina or Sunderland flying boats for conversion. In July 1942 five Sunderlands had been selected for modification. These were JM714, JM715, JM716, JM717 and JM718. The manned chariot was slung under the wing and held by crutches cantilevered out from the hull, to be lowered into the water and joined by the charioteers, who were carried with their dressers inside the aircraft. The wings holding the electrically operated lifting gear were reinforced to take the huge weight.

The work was carried out at Short’s aircraft works, Rochester, and JM714 was delivered to the Marine Aircraft Experimental Establishment, at Helensburgh. On 9th July Flight Lieutenant H. Pipes, with senior scientists, tested the modified Sunderland, then on 14th July flew to Bowmore, on the remote island of Islay.

The five expensively modified Sunderlands never saw active service because, somewhat belatedly, it was realised that there were major flaws in the scheme. The manned chariot relied on stealth and surprise, but the tremendous roar of the Sunderlands’ engines would alert the enemy. Still water had the effect of acting like a mirror; consequently landing this giant seaplane on a moonlight night was another hazard. Finally, the aircraft would be expected to collect the charioteers, often at daybreak, but lingering in enemy territory was out of the question because patrol boats would soon spot this giant seaplane.

On all but the first mission, British chariots were transported by submarine, and fitted to their casing was a pressure-tight container. The T Class submarine was selected for chariot transportation, and instructions were given for three containers to be fitted to Trusty, Turbulent, Trooper, Thrasher and P-311, two to Thunderbolt, Truant and Trident, and one to Taku. Despite these instructions, in October 1942 only Thunderbolt, Trooper and P-311 were converted to carry containers.

The machines sat on a small trolley on rails inside the container, fixed to a battery-charging point and air-charging point, and held in position by a securing bar and strops. The solid, watertight door was hinged at the top, lifting out of the way to allow the divers easy access to release and pull the machine from the container. With these additional compartments each submarine had to carry full Q tanks and adjust its ballast.