Stickleback-class submarine

Royal Navy Flag Midget Submarines 1954-1966
Cold War British Submersibles:
T class streamlined | Amphion class | Explorer class | X51 class | Porpoise class | Oberon class | Upholder class
HMS Dreadnought | Valiant class | Churchill class | Swiftsure class | Trafalgar class | Resolution class | Vanguard class

The Stickleback-class were midget submarines of the British Royal Navy, as a replacement of the WW2 XE-class submarines. They were essentially target submarines, designed to improve British ASW defences against midget submarines, as it was believed the Soviet Union whether had them or was about to develop such craft. But in a budget-stripped context, the Royal Navy also developed plans to make them carry a 15-kiloton nuclear naval mine (Red Beard programme, then Cudgel) into Soviet harbours as an early deterrence. This was unsuccessful, however, the fissile material were just too costly at the time. A proper deterrence program was later developed, and the Stickleback saw little service once the training procedures had been written, and when it was believed that no midget sub entered service with the Soviet Navy after all. They were scrapped in 1966, barely after nine years.


The idea of midget submarine is not new. One can argue it went back to the very origin of these boats, in the 1860-1890s before larger, more standardized boats started to appear. In WW2 they were still a thing, Italy, Germany, Japan, and Britain all had some. In 1944 Germany saw these as desperation weapons, the bare minimum to carry torpedoes, Italy and Japan made them to attack ports, carried by larger mother submersibles. Britain was impressed by the actions of X-Mas flotilla against its Battleships in Alexandria and started to consider their use to destroy the Battleship Tirpitz, their main concern in Norway. This led to the design of the “X” boats. They were designed to sneak in the Altafjord and drop mines under the battleship’s keel. They were used in 1944, but with mitigated success. 20 were made, soon replaced by the improved XE class in 1944-45 (15 made). They were used against the IJN in Singapore (Operation Struggle).

In the early 1950s the concept was not dead as they were still now Soviet ports to be cared for. This led to the design of the Stickleback-class submarines, the last British midgets. They were classified for decades. It had previously been assumed that they had been ordered as replacements for old XE-craft, but declassified papers in 1994 showed their development was more complicated. In 1954 indeed their main reason of being was to carry a nuclear sea mine to place in the approaches of prominent Soviet naval bases, such as Kronstadt in the Baltic or Sevastopol. These boats were to carry two detachable two-tons mines and at first it was envisioned to have a single payload underbelly, the centre section of the RAFs Mk 1 “Blue Danube” which was a 10,000lb bomb rated for 20kt but in 1955 it was modified for a ‘Red Beard’ program smaller 2000lb A-bomb.

The new Staff Requirement for the program was the “Cudgel” sea mine. At the time by December 1954, the Stickleback-class submarine still were called the X51 class. These were supposed to operate in proximity to base and drop their atomic payload at the depths down to 90m. This bomb had a setup timer which worked by half-hour intervals, detonating up to 12 hours after laying or even longer, based on 12-hour intervals up to seven days after laying. But the program, which competed with other nuclear bomb programs in Britain at the time, monopolized just like in the US by the RAF, had to secure access first to fissile material. However, its shortage made it simply unaffordable. “Cudgel” was cancelled between late 1955 and mid-1956 but the midget submarines built for them became essentially target ships… Thus, only four were made.

Design of the class

3D model on CGtrader

Hull and general design

Original plans – src, link below
The X51 class obviously derived from previous X-crafts. She was a simple unitary pressure hull with a keel, two side ballast blisters, and a flat deck, no conning tower but a persicope mast apparatus and a snorkel. The crew of 5 worked inside, one officer, two NCOs and two sailors. The absence of torpedo tube and everything usually found in a large submarine made it simpler.


She combined a complex arrangement, and all three components were small and serviceable inside the submarine. There was the main single prop (under fairing) shaft diesel electric. It was driven by a Perkins P6 6 cylinder diesel engine which developed 55 bhp and fed an electric motor to dive, rated for 44 shp. Aft the had two horizontal diving planes close to her propeller under fairing and another cross-arrangement tail aft of the propeller, four bladed. She also had a collapisible navigation masts with lights, radio set, a prism navigation mast forward of her main mast.


She carried a useful payload on her sides, strapped alongside her ballasts. This was not the initial plan however:
Programme RedBeard:
Red Beard was the first British tactical nuclear weapon, to be carried under belly by an English Electric Canberra medium bomber and later by the three “V” bomber (Valiant, Vulcan, Victor) and in the Navy by Supermarine Scimitars as well as the de Havilland Sea Vixens and Blackburn Buccaneers of the FAA. Operational Requirement OR.1127 1961, service in 1962. Replaced by the WE.177 in the early 1970s, withdrawn from service in 1971. In the X51 case, it was to be carried underbelly. There were concerns about the massive trim issues that would have compromise the safety of the submarine, the bomb was just too heavy. The Red Beard measured 71 cm (2 ft 4 in) in diamater for 3.66 m (12 ft) overall, but it would have been carried without its tail or head so probably around 2.50 meters or 8.2 feet. The warhead was at that stage the Mark 2, with a yield of 25 kilotons.

Programme Cudgel:
Cudgel was the real program under which was developed in secrecy the carrier midget submarine, a unique case probably in any navy. The Royal Navy planned to carry it with a midget sub inside Russian harbours as per documents newly released at the Public record Office in 1994, declassified. It was planned of dropping it and detonating with a long timer already detailed above. It seemed to answer the more desperate need of deterrence by default of having SSBNs, which had to wait for another declade. The British Admiralty like the USN at the time, denounced the monopoly of the bmb given to the air force; and the RAF indeed seems to have it with the V-bomber force.
By 1955, the “atomic” X craft was discussed and Operation Cudgel was to give the Navy a quick share of deterrence and slice of the massive budget devoted to nuclear strategy. In 1952 the first test was to place the bomb in a boat in the Monte Bello Islands off Australia. This, too was declassified in 2020. To keep secret for Cudgel all records were written by hand and led by Capt. P.J. Cowell, director of Undersurface Warfare. He however ultimately admitted that

“the existing X-craft as built today (is) too complicated and too large for the purpose. A specially designed craft is necessary, whose sole function is to deliver the atom bomb and return the crew to the parent (submarine).”

Detailed requirements for the new X-craft showed these to go for a drop-off point off an enemy coast, carried by a mothership, a Porpoise class submarine. Once released they had to make the final 150 miles (241 km) to the intended target. The crew had to prime, arm and detach their ‘Red Beard’ nuclear weapon from the inside. It could float in relatively shallow water and had to detonate up to a week after delivery, but there was no external contact, so no cancellation. It was also setup for very low temperatures, notably Murmansk and Archangel.
Albeit the X-craft were truly ready ready by 1957-1959, and the project apparently started well after all issues were solved. However if the Atomic Weapons Research Establishment at Harwell, Oxon . did not opposed to the idea, A.J. Sims, DNC, wrote that he did not believed that a conventional submarine, built using a non-magnetic material wit great endurance required could be made. In July 1956 however, Patrick Nairne (Secretary to the Board of the Admiralty) concluded that the programme should be terminated. With it, the whole X-craft development ceased as well.

⚙ Stickleback-class specifications

Displacement 35.2 tons surfaced, 39.27 tons submerged
Dimensions 53 ft 10 in x 6 ft x 7 ft 6 in (16.41 x 1.8 x 2.29m)
Propulsion 1 shaft diesel electric, one Perkins P6 6 cyl diesel, one electric motor, 50 bhp/44 shp
Speed 6.5 knots (12.0 km/h; 7.5 mph) surfaced, 6 knots (11 km/h; 6.9 mph) submerged
Range Diesel oil: 1.2t. Classified.
Max depth 295ft (90m)
Armament 2 detachable 2-ton side charges, see notes
Sensors Type 151 sonar
Crew 5

Royal Navy ww2 X51 Stickleback

HMS X51 at IWM Duxford, later she was transferred to the new Scottish Submarine Museum.
X51 Stickleback was started in 1951 but work proceeded slowly, and the submarine was not launched until 1 October 1954, 12:30hrs. She only served to train with a mockup of her future wezapon until the program was abandoned and then sold to the Royal Swedish Navy in 1958. There, she was renamed Spiggen (Swedish name for “Stickleback”). Spiggen at the time was assimilated to the “XE class” and denominated XE51 Stickleback when purchased. Its task in Swedish service was mainly to transport attack divers for sabotage and intel operations in Soviet waters. This is one of the declassified programme of the Swedish Navy, despite is neutrality. Ultimately, Sweden decommissioned her in 1970. She stayed in Sweden for a few years and returned to the UK as the country possessed none of the “X-types”. After display at the Imperial War Museum Duxford, storage at Portsmouth Naval Dockyard, X51 was carried to Faslane in September 2016. There, she became the centerpiece of a new museum exhibition and events site (see the link below) the new Scottish Submarine Museum at Helensburgh.

Royal Navy ww2 X52 Shrimp

HMS X52 was launched in October 1954, and scrapped 1965. Presumably she had been laid down also in 1951, and she served to train ASW crews against midget subs after the associated nuclear program was shelved.

Royal Navy ww2 X53 Sprat

HMS Sprat berthing alongside Training ship HMS Worcester, June 1957. src
X53 was launched 30 December 1954, loaned to US Navy 1958 (still classified information i can’t find anything on her during that time), she was scrapped 1966.

Royal Navy ww2 X54 Minnow

Minnow, launched 5 May 1955, scrapped 1966. Again, no detailed records for her few years of service.

Read More/Src


Paloczi-Horvath, George (1996). From Monitor to Missile Boat Coast Defence Ships and Coastal Defence since 1860. Conway Maritime Press.
Preston, Antony (2001). The Royal Navy submarine service : a centennial history. London: Conway Maritime.
Gardiner, Robert; Chumbley, Stephen (1995). Conway’s All the World’s Fighting Ships 1947–1995. NIP

Links stickleback-class.html
X-51 is here! Helensburgh museum’s submarine arrives in Scotland”. Helensburgh Advertiser. 9 September 2016. X class Stickleback-class_submarine


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