T-class Streamline (1950)

In 1945, the German Type XXI represented such a revolution in submarine design that it cannot be ignored and all nations able to built submarines jumped on the bandwagon of new constructions and upgrades to this standard some authors called the transition between “submersibles” and “submarines”. The US had their “GUPPY” conversions, and Britain had it’s “T” and “A” streamlined. In this first post we will see what happened to the WW2 T class submarines that were so converted in the cold war: The eight boats of the Taciturn and Tabard sub-groups, and the more austere five “Talent” sub-group conversion, for twelve conversions total. This extended their useful life to the 1970s.

Development

From 1951 a series of improvements was put in hand. Those with riveted hulls were limited in diving depth, and got the ‘T” class ‘Streamlined’ conversion. This involved fitting new batteries, streamlining the conning tower into a new ‘fin’, and reshaping the bow casing to give higher speed. Both these boats and the unmodernised ones had the ‘snort’ (snorkel) mounted on the port side, hinged at deck level. The 20mm gun was removed from all, but several retained their 4-in guns.
Tactician, Telemachus and Thorough were lent to the Royal Australian Navy in 1951 for ASW training, but remained under RN control. Tapir and Taurus became the Netherlands Zeehund and Dolfin from June 1948 to June 1953 and then reverted to the RN; they were scrapped in 1966 and 1960 respectively. Truculent was run down by the Swedish tanker Divina in the Thames Estuary on 12 January 1950 and sank with heavy loss of life; she was salved two months later and scrapped.
The class differed widely in appearance, some retaining the deck gun and others having a streamlined fin and modified casing. The 6th group had welded hulls and so most underwent a full modernisation from 1951.

HMS Tabard and Trump, the last two and best “super-T” conversions. The streamlining was the most advanced. If they look like the “A” class streamlining conversion or the later Oberons, it’s not random, they were the trailblazers. 2/2/1967, at Bluff NZ, coming from Dunedin. Credit: shipsnoslalgia.

Postwar, all surviving Group 1 and 2 boats were scrapped. The remainder were fitted with snorts. Then from 1947 the new threat posed by the USSR caused some concerns about the use by the Soviet Navy of ex-Type XXI, which were a new standard of much faster underwater submarines, streamlined. When it was confirmed the next year, it was planned by the admiralty to build a new generation of submarines, but also modernize the one it had, as the USN as just starting to do with its legacy Balao and Tench class boats.

The idea to streamline the T class was an obvious one as the latter were the largest, long range in the inventory. They were built from welded hulls for most and has extra room for upgrade. It was decided to improve the hill to reach greater underwater speeds, quieter, and press operation against Soviet submarines. This new role of hunter killer was a complete doctrinal change from their WW2 traditional anti-surface-ship role.

Early T class conversion as example. Gouache of HMS Taciturn in this configuration

In January 1948, this main operational function was made official. They were tasked to intercept Soviet submarines slipping out from Northern Russia to the northern Atlantic, preying on British and Allied merchant lines. In April 1948, the Assistant Chief of Naval Staff, Rear-Admiral Geoffrey Oliver, proposed in a document which circulated in the naval staff, that British submarines needed to be modified to take a more proactive role as well, of attacking Soviet submarines off the Northern Russian coast, and mining the waters close to their base to prevent any sortie in the first place. This was also a calculation resulting of the postwar budget cuts with many submarines being decommissioned. It was easier to be proactive and reduce the number of Soviet subs that could venture out of these constricted waters, rather than trying to intercept them all afterwards, when “diluted” and spread out in the Atlantic. This was a method called upon for “getting to the enemy on his home ground.”

Conversion Designs

HMS Trump, one of the “super T”. With her final sail, she looks like the next Porpoise/Oberon classes

The work carried out on these submarines was delayed also for the results of measurements using HMS Tradewind, modified between July 1945 and September 1946 as an acoustic trials submarine. This was the first “T streamline”. It had its external tubes and guns removed, and the conning tower completely faired out. The hull was much streamlined (angles were eliminated, the surface was smoothed out, water intake scopes were eliminated) and the remainder internal torpedo tubes blanked over so that no extrusion was left.
HMS Tradewind was well tested in 1946-48, and the results were used to create a new conversion standard.

The “super T”

From 1948, eight brand new late production all-welded boats were selected for conversion. This was called the “Super-T” conversion at Chatham Dockyard. These modifications included the following:
-Removal of deck guns
-Replacement of the conning tower with a “fin” (further improved)
-Smooth-surfaced, symmetrical, streamlined hull overall with elimination of all angles.
-Extra battery installed below the control room
-New hull section inserted* for an extra pair of motors plus switchgear.
-Diesel engines modified and supercharged at 300 bhp (224 kW).
-Bow reshaped.
-Section ranging from 14 feet (4.3 m) in the first batch of 4, then 17 feet 6 inches (5.33 m) in the late batch.
Performances:
Tested underwater speed of 15 knots (28 km/h; 17 mph), endurance 32 hours at 3 knots (5.6 km/h; 3.5 mph).
The additional electric motors were accommodated by cutting through the pressure hull and adding in a new 20 ft (6 m) hull section aft of the control room.
HMS Taciturn was the first to be modified in November 1948 until March 1951, followed by HMS Turpin in June 1949 to September 1951.
The programme was completed with the conversion of HMS Trump in February 1954 to June 1956.

The conversion was not a complete success: Their metacentric height was reduced, so they rolled heavily while surface in rough weather. In 1953 in the later conversions, increasing the buoyancy was done, by raising the capacity of the main ballast tank by 50 tons, merging these with an existing emergency oil fuel tank. For the four ones to be converted, it was decided to increase their buoyancy was lengthening the extra hull section from 14 to 17 feet 6 inches. This also enabling to enlarge the control room but with the catch no new heavy equipment was to be allocated to this space, to not degrade buoyancy and top weight. So this seriously upgrade potential on the long run.

The “Austere” Upgrade

Late “super T” conversion plans src
By December 1950, the further streamlining of five older riveted boats was approved, but in a more “austere” upgrade:
-Removal of deck guns and external torpedo tubes.
-Replacement of the conning tower by a simpler “fin”.
-Replacement of the batteries by more modern versions for 23% increase in power (this traduced by a 0.5 knot improvement).
-No new section added, and the hull remained the same, 83.4m overall long, 8.1m wide and 4.8m in draught.
-This limited work could be done under normal refit. The first of these “limited streamlined” riveted boats was HMS Tireless in 1951.

The last operational T class in the RN was HMS Tiptoe, decommissioned on 29 August 1969. The last non-operational was HMS Tabard, permanently moored as a static training submarine, at the shore establishment HMS Dolphin 1969-1974, until replaced by HMS Alliance.
However beyond Britain, the very last operational boat anywhere was the INS Dolphin, formerly HMS Truncheon, sold to the Israeli Navy and decommissioned only by 1977 when the new Gal class were available. INS Dakar, was lost and of her wreck was discovered in 1999, the accident cause remains uncertain.
Note: These will be a dedicated post on these conversions in 2026 or 2027.

Powerplant

“T-Conversions”

These eight boats, converted into two groups, were displaced after conversion 1,261, up to 1,460 tonnes surfaced or “normal” and from 1554 to 1588 to even 1734 tonnes submerged, with differences between the two sub-groups. Thhey were powered by the original two shafts and a new diesel-electric arrangement with four supercharged ASR diesels and four Vickers electric motors for a total of 2800 bhp surfaced and 6,000 shp when underwater. This traduced into 14 knots surfaced and 15.4 kts underwater, twice as much as a regular T-class. They carried 200t of oil for a range assimilated to 8,000-11,000 miles at 10 knots.

“T-streamline”

These boats had the same arrangement wit two ASR diesels, but only two electric motors for 2500 bhp compared to 1450 shp, traduced into 15.25 knots surfaced and 9.5kts submerged, balically the same figures as the Group III of WW2. Hence the “austere” conversion. They lacked the extra section and like the original T-class, displaced 1,090t surfaced and from 1,424 to 1,571 tonnes underwater.

Armament

The straemlinging forced the elimination of all external tubes, leaving only four bow, two stern. Some boats retained their QF 4 inch (100 mm) deck gun forward, either at completion, or until decommissioned. See the WW2 T-class for more.

Mark VIII** TORPEDO

Same classic model used by the T-class in the 1950s before new models were developed. Weight 1,566 kg (3,452 lb) for 21 ft 7 in (6.579 m) in lenght, powered by a Brotherhood burner-cycle engine for a range of 4,570 m at 45.5 knots or 6,400 m a 41 knots, carrying a 365 kg (805 lb) Torpex in straight course.

Mark 20 “bidder” (S)

The Mark 20 “bidder” electric torpedo was very promising model intended to be installed on the T-class streamlined. The (E) was a variant for surfaced ships and (S) for submarines. It had a single-speed setting at 20 knots, for a range of c12,000 meters. In the end only the E equipped briefly Rothesay and Whitby class frigates, but issues with their programming meant it was never fitted. Instead the S types was developed further and became the Mark 20 Improved entering service in 1971. Some Mark 20S remained operational in submarine service until the 1980s. There were also the Mark 20C and Mark 20I with 7,200 yd (6,600 m) and 14,000 yd (13,000 m) respectively at 20 knots.
Specs:
Mass 1,810 lb (820 kg), 13.5 ft (4.11 m) long x 21-in (53 cm)
Warhead: Torpex 196 lb (89 kg).
Engine: Electric, Battery using perchloric acid.
Performances: 12,000 yd (11,000 m) at 20 knots (37 km/h), max depth 800 ft (240 m)
Guidance system: Passive sonar

Mark 23 “Grog”

Designed started on a new electric torpedo on 1956. It was basically a wire-guided version of the Mark 20 with dual-speed mode for target approach and final run. First tests started in 1955. After the “Mackle” project was cancelled in 1956 all assets were transferred to complete the “grog” program. Production started in 1959. This successful model was largely produced and distributed on all British conventional submarines and remained operational until 1987. They became the main supply for the T-class, with a complement of Mark 8 after the Mark 12 “Fancy” project was abandoned against surface ships.
Specs:
Mass 2,000 lb (907 kg), length 14.9 ft (4.54 m) x 21 in (530 mm)
Warhead: Torpex, 196 lb (89 kg)
Engine: Electric, perchloric acid battery.
Range 12,000 yd (11,000 m) on low-speed 20 knots approach, and 8,900 yd (8,100 m) high-speed run 28 kn (52 km/h)
Guidance system: Passive sonar and Wire guided.

M type Mark II Mines

The M Mark II were designed in WW2 as “Type G” as sub-launched ground mine, two replacing a torpedo. They used a CR magnetic trigger. Production was halted in November 1942 with 1,310 made and in storage. They equipped T, S classes as well as A class postwar. The T class carried 12 of them in complement to their 20 torpedoes in order in case of war, to mine the entrance of Soviet Ports.
Specs. Mark II M Weight 1,760 lbs. (798 kg), payload 1,000 lbs. (454 kg) minol charge. Laid at 8 knots in 5-60 fathoms (9-110 m).

Sensors

It seems like for the streamlined A class, they had the sonar Type 186, 187 and 197 (the bulbous appendage on the bow). The Type 186 was installed in the 1950s. This was an active search radar, with 12 double hydrophones either side and a signal processed into frequency bands of 300-600 Hz and 600-1200 Hz, displayed on a paper record via four pens representing each frequency band, each side.
The 718X was given a low-power-active mine detection capability, reclassified as Type 187, the “Attacker” sonar, on the nose, under a typical 16′ x 6′ x 4.5′ large dome.
The last complement was the Type 197 “watcher”, from the abandoned Type 196 in 1959. The 197 entered service as a true passive sonar in 1962, possibly equipping some of the early eight boats. Indeed, some were discared already in 1964-68.
There was also a search and a navigation radar, likely of the same type carried by the Amphion class.

⚙ specifications (Tabard Group)
Displacement	1460t standard, 1588t/1734t submerged.
Dimensions	285/293 ft x 26 fr 7in x 16ft (89.5 x 8.1 x 4.9m)
Propulsion	2 shafts 4 supercharged ASR diesels, 4 EM 2800/6000 hp
Speed	14/15.4 kts
Range	oil 200t, c9000 nm at 10 kts
Armament	6 TTs (4 bow, 2 stern, 20 torpedoes, 12 Mk.2 mines)
Max depth	As T class
Sensors	Type 186, 187, 197 sonar suit +search/nav radar
Crew	68

Career of the “Streamline T”

HMS Tabard (src ships-nostalgia)
In 1951, Tabard was taken in hand for a radical reconstruction. Her pressure hull was cut at the after end of the engine room. A new section was addeded there of 20 feet (6.1 m). This helped installing an additional battery compartment and two more electric motors. No longer direct, the powerplant became a diesel–electric transmission. HMS Trump was also modified that way, and her bridge was made into a streamlined fin, which was another novelty at the time. All external fittings were removed (see the streamlined T conversion below), and the periscopes, radar masts, snort mast and wireless mast were now enclosee flush with he top of a completely new, well faired bridge fin.

In 1960, Tabard, Taciturn and Trump were sent to the 4th Submarine Squadron in Sydney, refitted at Cockatoo in 1961-1962 and served with Far East Fleet, RAN and RNZN. By April 1963 she collided with a wharf when docking in Brisbane. On 8 May she collided with HMAS Queenborough (at periscope depth), repaired in Sydney, HMAS Kuttabul. On 10 February 1964, she she was in ASW exercise as the prey for HMAS Melbourne and HMAS Voyager and later helped to rescue the crew of the latter when she was cut in half after being rammed by the carrier by accident. Tabard took part in the NEWS EX exercise in Hauraki Gulf and was refitted 1964-1965, then joined the newly formed 1st Australian Submarine Squadron in 1967 on loan to the RAN before new subs arrived. She was back home by March 1968, moored as static training hull at HMS Dolphin 1969-1974, replaced by HMS Alliance and decommisioned, last T class in service, sold for scrap on 2 January 1974.

HMS Truncheon in Feb. 1964
Back home from the Pacific, she she was converted as a “T streamlined” and remained in operation against Soviet subs of the north sea. Surplus, she was sold to the Israeli Navy in 1968, renamed INS Dolphin, just like HMS Turpin and HMS Totem, commissioned into the Israeli Sea Corps and eventually scrapped in 1977 as the one and only last T class submarine in service.

HMS Thermopylae in the late 1950s src
Postwar, Thermopylae trained with the 3rd Flotilla in the Holy Loch. On 15 January 1950 she ran aground on Stevenson Rock (Skerryvore, Inner Hebrides). In 1953 she was at the Coronation fleet review. She was in service until December 1968, sold for BU at Troon in 1971.

Otem was part of the late “super T-conversions” between 1951 and May 1953 at Chatham. Her airguard radar aerial was also removed.
Under Commander John Coote in exercises easy, she left her hunting escorts “in the dust” as she made a mile in four minutes at 18 knots (33 km/h) and could stay ten minutes silentl at 12 knots (22 km/h) making 3 miles (4.8 km) away. In 1953 she took part in the Fleet Review. By early 1955 she was at “Operation Defiant” in the Barents Sea, to gather Signals intel. on Soviet naval forces. She was however detected and depth charged, crash dove to 280 feet (85 m) to evade but drifting into a minefield. She was unharmed and came back home. She was refitted at Malta in 1961-1963, recom. at HMNB Portsmouth with a new crew from 28 January, 1st Submarine Flotilla, Gosport. In Halifax in the 1945 she was presented a totem pole by the Cowichan Tribes in 1945, later stolen when she was in Halifax, Canada. She was fitted to the front of her bridge fin while in harbour. She was sold to the Israeli Navy in 1965, as INS Dakar, but famously sunk during transfer.

HMS Turpin was fitted with a snort mast and in 1955, was in the arctic circle on an ELINT mission (listening to specific frequency bands of Soviet radars). They were nearly rammed by a Soviet Navy surface vessel, making a crash dive was ordered and later taking refuge in a cold water line to evade their sonar and escape. She was was sold to the Israeli Navy in 1965, renamed INS Leviathan (after the biblical sea monster), commissioned into the Israeli Sea Corps in 1967 and scrapped in 1978, the very last T class still in service anywhere in the world. Too bad she was not preserved.

Postwar she was one of the streamlined T-class and she was one of two submarines with HMS Tabard, which bridge was incorporated into the added fin section, and last converted. In 1960 with Taciturn and Tabard se was with the 4th Submarine Flotilla at Sydney, Far East Fleet, and oparting to train ASW vessels of the RAN/RNZN, as well as “NEWS EX” exercise in the Hauraki Gulf, New Zealand. She had refits at Cockatoo Dockyard in 1962-1963, 1965-1966.She became the last T class on station in Australia, departing on 10 January 1969, privisionally as part of the 1st Australian Submarine squadron, waiting for the new Oberon class under construction to arrive. Back home she was scrapped at Newport from 1 August 1971.

Tiptor was already a very succeful WW2 veteran. In 1947 she was inspected by George VI, brought him underwater, and surfacing, firing her deck gun. In November she followed 7 subs and HMS Opportune in ASW training for two weeks. In 1951 she was rebuilt as a “streamline T”. She also took part in the 1950 film ‘Morning Departure’ directed by Roy Ward Baker with HMS Maidstone as mother ship. In 1952 was presented ballet dancer Moira Shearer ballet shoes after the 1948 film “The Red Shoes”. While at Tromsø on 18 July 1955 she collided with a coastal steamer, the 2,162 GRT Nordlys, entering the harbour, after colliding already with the destroyer HMS Chevron. This the destroyer in turn collided with Tiptoe, which snapped her moorings, and pushed halfway under a wooden quay.
She took part in escape trials in 1962 off Malta, from extreme depths, 233 feet (71 m), with ascent rates of up to 6.6 ft/s (2 m/s), testing buoyant ascent suits. Chief Petty Officer Christopher Crossman was awarded a commendation, LtCdr L. Hamlyn was awarded an OBE. After refit in Portsmouth, on 10 January 1964 in heavy fog she ran aground 40 yards (37 m) of her intended mooring. Divers assessed the damage, found none. She was refloated by the evening tide, pulled off by tugboats. LtCdr David Brazier, first command, was severely reprimanded for negligence at his court-martial. She later was damaged in a collision with HMS Yarmouth on 13 July 1965 while under periscope depth, 10 miles (16 km) southeast of Portland Bill.
LtCdr Charles Henry Pope was severely reprimanded for 4 counts of negligence. Her final commission was on 24 February 1967, with six ballet dancers from the Royal Ballet attending her departure ceremony, and she was reported by the press as the oldest Royal Navy submarine, making an apparition at Portsmouth Navy Days. She was decommissioned in 1969, last ever T-class with a ceremony at Spithead on 29 August with 13-year-old ballet dancer Judy Wright dancing on her upper deck. She was sold in 1971, scrapped at Portsmouth, 1975. Unfortunately she was not preserved, bu her anchor was in Blyth, Northumberland and her oak nameplate is used in port and ceremonial occasions.

Postwar, she one of the first to undergo the ‘Super T’ streamlining conversion. On 9 January 1958, she ran aground in the Firth of Clyde, was refloated, helped by the boom defence vessel HMS Barcombe. After a eventless career she was decommissioned and sold to Thos. W. Ward, scrapped at Briton Ferry in Wales by 8 August 1971.

HMS Talent, src clydemaritime, colorized
Postwar, Talent was sent in the Far East after and later back home, spent time at the mediterranean stations. In 1953 she was part of the Coronation Fleet Review. On 15 December 1954 she was washed out of drydock at Chatham Dockyard, not found until the following day, causing four death. After this, all caissons at Chatham on the river affected by tidal forces were chained down to prevent them lifting, inspected more regularly. She was refloated, repaired and converted as a streamined “super T” between 1954 and 1956. But soon she was again damaged in collision while diving off the Isle of Wight, on 8 May 1956. She was later used for publicity trip around the south and east coasts by October 1960, and iopened to public, visited by 33,000+. Refitted at Malta in 1960-1961, she remained in the Mediterranean until May 1962 and took part in Portsmouth Navy Days in 1965. She was decommissioned on 19 December 1966, scrapped at Troon in Scotland 1 February 1970.

Only commissioned on 15 December 1945 with the Pennant number P328 she was still training when WW2 ended in home waters. In 1953 she took part in the Fleet Review. She was modernised at Devonport Dockyard in 1955, based at the Home Station and Mediterranean, with refits at Malta. In 1965 she was in the 1st Submarine Squadron in Portsmouth, providing training to submarines crews and took part in Portsmouth ‘Navy Days’. On 20 August 1967 while on exercise off the West coast of Scotland she towed the powerless, adrift Danish merchant ship Opnor, preventing her drifting onto a reef. She was sold for scrap at Cairn Ryan in March 1970.

In 1951 she was the first streamlined at HM Naval Dockyard, Devonport and recommissioned in 1953. She took part in the Fleet Review to celebrate the Coronation of Elizabeth II, showcasing her concept. She had a second modernization by late 1950s at Chatham Dockyard. In 1959 she took part in ‘Navy Days’ in Portsmouth. From 1960, she was commanded by Sandy Woodward, future admiral leading the fleet in the South Atlantic during the 1982 Falklands War. In service until August 1963 she was sold for BU, BU in 1968.

Tapir postwar was transferred to the Far East, Fremantle base via Gibraltar, Malta, Port Said, Aden, Trincomanlee, and the Malaya-Burma-East Indies sector. But preys were rare, apart sampans. She was still in exercizes when the war ended in August. On 18 June 1948, she was surplus to requirements, loaned to the Netherlands for five years as HNLMS Zeehond from 12 July and purchased at the end of the loan.

Commissioned too late to see the war, postwar (construction suspended), she was under command of Gordon Tait in 1947-1948. In 1953, she was at the Fleet Review celebrating the Coronation of Queen Elizabeth II. After a spotless career, not converted as a full “streamlined T” but rather given the austere conversion, she finally decommissioned, sold and scrapped at Briton Ferry, Wales on 5 June 1965.

Read More/Src

Books

Paul Kemp’s “The ‘T’ class Submarine”: The Classic British Design (1990). ‎Naval Institute Press.

Links

rnsubs.co.uk/
rnsubs.co.uk development streamlining
warhistory.org/@ hms-taciturn-on-station
battleships-cruisers.co.uk
rnsubmusfriends.org.uk
British_21-inch_torpedo Mark_20_Bidder

Videos

On naval history with Dr. Alex

Model Kits

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3D

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