The A- and B-class destroyers were a group of 18 destroyers built for the Royal Navy during the late 1920s, with two additional ships built for the Royal Canadian Navy. The British ships were divided into two flotillas of eight destroyers, each with a flotilla leader.

Design and description The A-class design was derived from the 1926 prototypes and for the 1927–28 Naval Construction Programme. The initial staff requirements were unrealistic and would have resulted in a much larger, unaffordable ship; they were scaled back, both to reduce the size of the ship and to save money.Friedman, pp. 195–202 Nonetheless, the design had an improved gun armament, heavier torpedo armament, and greater range, at the cost of of speed, in comparison with the prototypes. The As were fitted with the Two-Speed Destroyer Sweep (TSDS) minesweeping gear and only had a residual anti-submarine ability while the Bs were equipped with Type 119 ASDIC (sonar) and had a full complement of depth charges, but could not use the TSDS.Lenton, pp. 150–152

This was the beginning of the Admiralty's policy of alternating TSDS and anti-submarine capabilities between destroyer flotillas.Lenton, pp. 150–152 The ships displaced at standard load and at deep load. They had an overall length of , a beam of and a draught of .Whitley, pp. 97, 99 The A class had a metacentric height of at deep load.March, p. 256 The ships' complement was 138 officers and ratings as built, but increased in size up to 162 during the war.March, p. 258

The destroyers were powered by two Parsons geared steam turbines, each driving one propeller shaft using steam provided by three water-tube boilers equipped with superheaters. Five of the As and all of the Bs had Admiralty three-drum boilers that operated at a pressure of and a temperature of while Ardent and Anthony were fitted with Yarrow boilers of pressure at the same temperature. Acheron was given experimental Thornycroft boilers that had a working pressure of and a temperature of to examine the weight and economy savings.Friedman, p. 198

Her specific fuel consumption was reduced from /hp/hour in her sisters to /hp/hour,Lenton, p. 151 although she was plagued by mechanical problems for her whole life.English, p. 19 In the event the trials were inconclusive, and the Admiralty continued to use the lower-temperature and pressure Admiralty three-drum boiler until the of 1942, nearly ten years after other major navies began to use higher-pressure and temperature boilers.Rippon, pp. 241–245 The turbines developed a total of for a designed speed of and the ship exceeded that during their sea trials.March, pp. 247, 260 The destroyers carried a maximum of of fuel oil that gave them a range of at .Lenton, p. 152

All of the ships had the same main armament, four quick-firing (QF) Mark IX guns in single mounts with enlarged gun shields, designated 'A', 'B', 'X', and 'Y' from front to rear. Although the A class were intended to be equipped with gun mounts that could elevate up to 40°, and 'B' gun on a high-angle mount capable of 60°, all four guns ultimately had a maximum elevation of 30°.March, pp. 247, 250, 252, 260 They fired a shell at a muzzle velocity of to a range of .Campbell, p. 48 Each gun was provided with 190 rounds. For anti-aircraft (AA) defence, the A- and B-class ships carried two QF two-pounder Mark II AA guns mounted on platforms between the funnels, each with 500 rounds. They were fitted with two quadruple mounts for 21-inch (533 mm) torpedo tubes. The A-class ships were initially going to be fitted with two throwers and four chutes for eight depth charges, but they interfered with the TSDS equipment so the throwers, one chute and two depth charges were removed.Friedman, p. 197 The Bs were equipped with two throwers and one rack for twenty depth charges.March, p. 260 While not initially fitted with ASDIC, space was reserved for it, and at least some of the As received it beginning in the late 1930s.English, pp. 17, 19, 24

The fire-control system for these ships was little advanced over their First World War-era predecessors. A pedestal-mounted, manually operated Destroyer Director Sight and a separate rangefinder positioned to its rear were situated above the bridge; the director transmitted training angles and firing impulses to the main guns, which fired at fixed elevations.The Dreadnought Project page on the British Destroyer Director of WW1 They had no capability for anti-aircraft fire and the anti-aircraft guns were aimed solely by eye. No fire-control computer was initially installed, but an Admiralty Fire Control Clock Mark II was retrofitted after it had been proven in the subsequent C-class destroyers.Campbell, p. 14; Friedman, p. 207; Hodges & Friedman, p. 10

Canadian ships The two Canadian ships (Saguenay and Skeena) were designed to be of a similar performance to the A-class ships to allow them to tactically combine. More flare was given to the bow to keep it drier and the forward part of the hull was strengthened to withstand ice. Their metacentric height was increased to allow for the build-up of ice and snow on the upperworks and they were shorter than their British counterparts. Although the ships had an additional of fuel, fewer horsepower and lacked superheaters for their boilers, they had the same range and speed as their brethren of the A and B classes. They displaced at standard load and at deep load. The ships were built by John I. Thornycroft & Company in Woolston, Hampshire and had the broad, slab-sided funnels characteristic of that builder.English, p. 26; Lenton, pp. 153–154

Flotilla leaders was built to an enlarged design to accommodate the commander of the destroyer flotilla, Captain (D) and his staff, some 47 additional officers and ratings. The ship displaced roughly more than the private ships ( at standard load and at deep load); she was longer overall and had a beam wider. She shipped a fifth 4.7-inch gun between the funnels, which forced the two-pounders to be repositioned abaft the rear funnel, and was not fitted with TSDS. To compensate for her greater size, Codringtons oil tanks were increased by and her turbines were rated at to give her the same range and speed as the private ships, but she proved to be significantly faster as she made during her sea trials. However, the increased length made her somewhat unhandy, having a turning circle much greater than the standard A class, which complicated manoeuvres with her flotilla.March, pp. 247, 258–259

Unlike Codrington, Keith was built upon the same hull as her sisters to save money and to make her tactically identical to her flotilla-mates. The initial proposal was to enlarge the aft deckhouse to make room for the Captain (D) and his staff at the expense of 'Y' gun and the TSDS gear, but the gun was reinstated while she was under construction. The ship was too small to accommodate the entirety of the staff, and Blanche was fitted as a divisional leader to carry the surplus.Friedman, p. 205; March, pp. 265, 267, Whitley, p. 99 Keith was heavier than the private ships at standard load and nearly heavier at full load ( and , respectively) and carried 19 additional officers and ratings.

Wartime modifications The initial wartime modifications were limited and mostly related to the survivability of the crew, aside from the addition of 50 rounds per gun of 4.7-inch ammunition and the increase of depth charge stowage to 42 (the Canadian ships carried 33). Beginning in May 1940, the after bank of torpedo tubes was removed in most ships and replaced with a QF 20-cwt anti-aircraft gun,"Cwt" is the abbreviation for hundredweight, 20 cwt referring to the weight of the gun. the after mast and funnel being cut down to improve the gun's field of fire.Friedman, pp. 233–236, 239, 241 Of the early war losses, only Codrington and Acheron received this modification before they were sunk.Whitley, p. 97 By October, all of the surviving A-class ships plus Beagle, Boadicea, Boreas and Brilliant had been modified and the rest of the Bs had received theirs by April 1941.Friedman, p. 241

Beginning in 1941, most ships had 'Y' gun and the TSDS gear replaced by racks and throwers for a pattern of 10 depth charges, with stowage increased to 70 charges. Their light AA armament was augmented by a pair of QF Oerlikon guns, one each abreast the bridge, and a Type 286 short-range, surface-search radar, adapted from the Royal Air Force's ASV radar, was also added. The early models, however, could only scan directly forward and had to be aimed by turning the entire ship. The Canadian ships replaced their two-pounders with a pair of quadruple machine guns and were not fitted with Oerlikons by 1942.Friedman, pp. 237, 242, 245; Lenton, pp. 152, 154

Late that year, some of the surviving ships were further modified into what became known as escort destroyers. These ships had either 'A' or 'B' gun replaced by a Hedgehog anti-submarine spigot mortar. Achates, Beagle, Boreas, and Bulldog were among the first ships to be so converted. Around this same time many ships had their Destroyer Director Sight and rangefinder exchanged for a Type 271 target-indication radar. Beagle and Bulldog were later fitted with a two-pounder bow chaser to engage German E-boats in the English Channel while Boadicea received two elderly six-pounder (57 mm) Hotchkiss guns to deal with U-boats on the surface at close range.Friedman, pp. 247, 252–253

Beginning in 1943, the three-inch gun was removed to allow for the installation of a Huff-Duff radio direction finder on a short mainmast; the aft torpedo tubes were sometimes reinstalled. The single 20 mm guns abreast the bridge were replaced by Mark V powered mountings for twin weapons later in the war, the singles replacing the two-pounder or .50 caliber guns amidships, with a further pair of Oerlikons that replaced the searchlight between the torpedo tubes.Friedman, pp. 242–247

Ships

A-class ships + Construction data Ship Navy Builder Laid downEnglish (1993), pp. 15, 26 Launched Commissioned Fate Royal Navy Swan Hunter & Wigham Richardson, Wallsend 20 June 1928 8 August 1929 4 April 1930 Bombed and sunk off Dover, 27 July 1940 John Brown & Company, Clydebank 13 August 1928 8 August 1929 11 February 1930 Sunk by the German battleships and off Narvik, 8 June 1940 11 September 1928 4 October 1929 11 February 1930 Sunk by the German cruiser in Battle of the Barents Sea, 31 December 1942 Hawthorn Leslie & Company, Hebburn 10 July 1928 9 July 1929 9 February 1930 Sold for breaking up, 7 July 1947 11 July 1928 27 July 1929 20 February 1930 Sold for breaking up, 28 January 1946 Scotts Shipbuilding & Engineering Company, Greenock 30 July 1928 24 April 1929 14 February 1930 Sold for breaking up, 21 February 1948 26 June 192914 April 1930 Sunk by the German battleships Scharnhorst and Gneisenau off Narvik, 8 June 1940 Vickers Armstrongs, Barrow-in-Furness 20 August 1928 22 August 1929 Damaged by the explosion of SS Fort Lamontee in Algiers, 4 August 1943, and written off as a constructive total loss John I. Thornycroft & Company, Woolston 29 October 1928 18 March 1930 13 October 1931 Mined off the Isle of Wight, 17 December 1940 Royal Canadian Navy 27 September 1929 11 July 1930 22 May 1931 Damaged in a collision 15 November 1942 and de-rated to training ship, sold for scrap 1945 14 October 1929 10 October 1930 10 June 1931 Wrecked in Kollafjord, Iceland, 25 October 1944

B-class ships