Britain was not far behind Italy in the development of midget submarines – and might have been in advance. As early as 1909–2, Lt Godfrey Herbert, RN, designed the Devastator, a one-man submersible which set the later style of British boats in being armed with a detachable explosive warhead. Submitted to the Admiralty in 1912, the boat was then (as later, during World War I) refused on the grounds that the operator’s survival could not be guaranteed; ie, that it was a suicidal weapon. However, it attracted the attention of Capt Max Horton, a submarine “ace” of World War I, who contributed suggestions for its improvement and was, according to his biographer, prepared to accept the fact that “the crew would have to be expendable”. Early in World War II, Admiral Sir Max Horton, as Flag Officer, Submarines, was to be a strong advocate of the development and deployment of British midgets.
Herbert’s design was not the only one to influence the British midgets of World War II. In 1915, Robert H. Davis of the Siebe, Gorman company patented a three-man boat incorporating an “escape” compartment. And in 1924, Max Horton himself put forward plans for three types: the A Type, based largely on Herbert’s designs; the two-man B Type, with a detachable compartment containing both warhead and main engines; and the C Type, armed with a single torpedo slung beneath the main hull. Although the C Type, met with some interest, none was adopted: the midgets were once again adjudged to be at best semi- suicidal craft.
All these design strands were woven together in 1939–40, when Admiral Horton learned that a private yard near Southampton was constructing a midget incorporating many features of earlier designs, including the Davis escape apparatus, to the plans of a retired submariner of World War I, Cdr Cromwell H. Varley. In spite of some opposition, Horton and Cdr Herbert (the same officer who had begun his own midget design in 1909) had Varley’s craft evaluated and subsequently improved by the Directorate of Naval Construction. It was to become the “X-craft”.
Characteristics of the “X-craft”
The prototype X-craft, the two-man X-3 and X-4, were built from early 1942 onward, and these experimental submersibles were quickly followed by the operational “X-5” class of 12 boats, which were to be the midgets that carried out missions in European waters. Without explosive charges (see below) an “X-5” midget displaced 27/30 tons (27.4/30.5 tonnes) and was 5.9ft (1.8m) in beam. The craft was 51.25ft (15.7m) long overall and 7.5ft (2.3m) in draught. A single-shaft 42hp Gardner diesel gave a maximum surfaced speed of 6.5kt (7.5mph, 12kmh), and a 30hp electric motor a maximum submerged speed of 5.5kt (6.3mph, 10kmh) – with explosive charges, in both cases. Maximum surfaced range was 1,320nm (1,518 miles, 2442km) with charges or l,860nm (2,139 miles, 3441km) without charges – at 4kt (4.6mph, 7.4kmh), in both cases. The craft carried a crew of four, one of them a trained diver.
The boat was divided into four main compartments. Forward was the “wet-and-dry” compartment, with a hatch from which the diver could leave the craft, to place demolition charges or to deal with underwater obstacles, and return when his task was completed. Also forward was the battery compartment, with the control room amidships and the engine room aft. Armament reflected the role for which the boats were chiefly intended: attacks on major warships at anchor. Unlike the torpedo-armed Japanese, Italian and German midgets the X-craft carried only detachable explosive charges. On each side of the boat, slung in a steel frame and streamlined to the boat’s outline, was a 4,400lb (1993kg) charge of Torpex. Released from within the X-craft, the charges sank beneath a target to become lethal mines, with clockwork fuzes running up to 36 hours.
Although the X-craft were stout boats of remarkable range and endurance – capable of diving safely to more than 300ft (91m), with a submerged endurance of 80 hours at 2kt (2.3mph, 3.7kmh), although with the necessity of rising to ventilate every 12 hours – their seaworthiness was limited by instability in rough weather and by the effect on their crews of long periods in such confined spaces. Thus, they were normally towed to the target area by fleet submarines, while manned by a passage crew; an operational crew travelled out on the mother boat and took over the midget for the attack.
Considering their efficiency, the X-craft were under-used; and some would ascribe this to the Admiralty’s equivocal attitude to what was still felt to be a semi-suicidal weapon. The major missions described briefly below will give the reader some opportunity of deciding for himself just how “suicidal” the X-craft were in comparison with the Japanese, Italian and German midgets. Meanwhile, it should be noted that X-craft also performed valuable services in such roles as reconnaissance of invasion beaches and the landing of clandestine agents. (Six boats of the “XT-class” were commissioned as training vehicles between June 1943 and March 1944; these were similar in most respects to the “X-5” boats, but were not fitted out for operational use; 12 were ordered but not built.)