The Type 15 and Type 16 Anti-submarine Frigates

At the end of the Second World War, each of the victorious allies took examples of captured Axis ships. Some were used for experimental purposes and others were incorporated into their respective navies as active units.

The Soviet Union managed to acquire a number of complete U-boats and up to eleven incomplete ones, and these included examples of the latest designs, the Type XXI. This was an advanced U-boat design that had been introduced into service just before the end of the Second World War. It had a streamlined hull as well as improved underwater performance, and it was designed to operate submerged for long periods, thus making it significantly more difficult to find and sink.

An example of a Type XXI U-boat, U-3008. She was handed over to the United States Navy and used by them until June 1948.

Four Type XXI submarines were commissioned into the Soviet Navy (U-2529, U-3035, U-3041, and U-3515 became B-27, B-28, B-29, and B-30 (later B-100) respectively). British and United States intelligence services estimated that by January 1948 the Soviet Navy had fifteen Type XXIs operational, could complete a further six more within 2 months, and had sufficient captured prefabricated components to build another thirty-nine within eighteen months.

This posed a major problem for the Royal Navy. The Type XXI could make 15.6 knots on the surface and 17.2 knots underwater and the top speeds of the Royal Navy’s escorts were (by class):

• Flower-class corvettes: 16 knots
• Castle-class corvettes: 16.5 knots
• Black Swan-class frigates: 20 knots
• River-class frigates: 20 knots
• Bay-class frigates: 19.5 knots
• Loch-class frigates: 20 knots
• Hunt-class destroyers: 27 knots
• Captain-class destroyer escorts (Lease-Lend): 20 to 24 knots

Only the Hunt-class ships had a sufficient margin of speed over the Type XXI to enable them to hunt and kill the Type XXI submarines that were operated by the Soviet Navy … but many were already worn out after heavy wartime service and some of the class had a reputation for being top-heavy and would not be suitable for rebuilding into fast anti-submarine frigates. The Royal Navy did – however – have a large number of destroyers that had been built to a standard design under the War Emergency Programme, and many of these were relatively new and in good condition.

It was therefore decided to rebuild a number of these ‘surplus’ hulls into anti-submarine frigates. Two designs were chosen: the Type 15, which was a major rebuild of the vessels chosen, and the Type 16, which was a much more austere conversion that could be undertaken quickly.

The Type 16 frigates were:

• O-class: HMS Orwell. HMS Onslow and HMS Onslaught had been transferred to the Pakistan Navy and became PNS Tippu Sultan and PNS Tughril respectively. They were later converted into Type 16 frigates for the Pakistan Navy.
• P-class: HMS Paladin and HMS Petard.
• T-class: HMS Teazer, HMS Tenacious, HMS Termagant, HMS Terpsichore, HMS Tumult, HMS Tuscan, and HMS Tyrian.
• W-class: HMS Wessex and HMS Whelp had been transferred to the South African Navy and become SAS Jan van Riebeeck and SAS Simon van der Stel respectively. They were later converted into modified versions of the Type 16 frigate for the South African Navy.

HMS Tenacious before her conversion.

HMS Tenacious after her conversion.

The class’s characteristics were as follows:

• Displacement: 2,300 tons (full load)
• Dimensions:
• Length: 362ft 9in (110.57m)
• Beam: 37ft 9in (11.51m)
• Draught: 14ft 6in (4.42m)
• Propulsion:  2 x Admiralty 3-drum boilers providing steam to two turbines powering two propellors
• Speed: 32 knots
• Complement: 175
• Sensors and processing systems: Type 293Q target indication radar; Type 974 navigation radar; Type 1010 Cossor Mark 10 IFF Type 146B search sonar; Type 147 depth finder sonar; Type 162 target classification sonar; Type 174 attack sonar
• Armament: 1 x twin 4-inch (102mm) gun Mark 19; 1 x twin 40 mm Bofors gun Mk.5; 5 x single 40 mm Bofors gun Mk.9; 2 x Squid anti-submarine mortar; 1 x quadruple 21-inch (533mm) torpedo tubes for Mk.9 torpedoes

The Type 15 conversions were far more extensive. The ship's existing superstructure was completely remodelled, and the changes included:

• The forward superstructure was extended across the width of the ship.
• The front of the superstructure was curved and reinforced to resist the impact of waves at high speed and in rough weather.
• The forecastle was extended aft to provide additional internal volume.
• The bridge was located at forecastle deck level.
• The operations room was located behind and below the new bridge.

The Type 15 frigates were:

• R-class: HMS Rapid, HMS Relentless, HMS Rocket, and HMS Roebuck.
• T-class: HMS Troubridge.
• U-class: HMS Grenville, HMS Ulster, HMS Ulysses, HMS Undaunted, HMS Undine, HMS Urania, HMS Urchin, and HMS Ursa.
• V-class: HMS Venus, HMS Verulam, HMS Vigilant, HMS Virago, and HMS Volage.
• W-class: HMS Wakeful, HMS Whirlwind, HMS Wizard, and HMS Wragler.
• Z-class: HMS Zest.
• Australian U-class: HMAS Queenborough, HMAS Quadrant, HMAS Quiberon, and HMAS Quickmatch.

HMS Ulster before her conversion.

HMS Ulster after her conversion.

The class's characteristics were as follows:

• Displacement: 2,700 tons (full load)
• Dimensions:
• Length: 358ft (109m)
• Beam: 37ft 9in (11.51m)
• Draught: 14ft 6in (4.42m)
• Propulsion:  2 x Admiralty 3-drum boilers providing steam to two turbines powering two propellors
• Speed: 31 knots
• Complement: 174
• Sensors and processing systems: Type 293Q target indication radar; Type 277Q surface search radar; Type 974 navigation radar; Type 262 fire control radar on director CRBF; Type 1010 Cossor Mark 10 IFF search sonar: Type 174 search sonar; Type 162 target classification sonar; Type 170 attack sonar
• Armament: 1 x twin 4-inch (102mm) Mark 19 gun; 1 x twin 40mm Bofors Mk.5; 2 x Squid or Limbo Mark 10 anti-submarine mortars
• Aviation facilities: A flight deck was fitted to HMS Grenville and HMS Undaunted for the Fairey Ultra-light Helicopter (HMS Genville) and Saro P.531 helicopter (HMS Undaunted). (N.B. The Saro P.531 was the forerunner of the Westland Wasp helicopter.)

The Type 15 and Type 16 anti-submarine frigates fulfilled a vital role in the Royal Navy. They not only filled a gap in the Royal Navy's anti-submarine capabilities at a time when Russian submarines based on the Type XXI U-boats (i.e. the Whiskey-class) were coming into service, but also gave the Admiralty and the Royal Corps of Constructors time to develop the design of the Type 12 anti-submarine frigates (the Whitby-class) which – in turn – was developed into the later Type 12M (the Rothesay-class) and then the very successful Type 12I or Leander-class.