Editing A- and B-class destroyer (section)

==Design and description==
The A-class design was derived from the 1926 [[prototype]]s {{HMS|Amazon|D39|2}} and {{HMS|Ambuscade|D38|2}} 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.<ref>Friedman, pp. 195–202</ref> Nonetheless, the design had an improved gun armament, heavier torpedo armament, and greater range, at the cost of {{convert|2|kn|lk=in}} of speed, in comparison with the prototypes. The As were fitted with the Two-Speed Destroyer Sweep (TSDS) [[minesweeper|minesweeping gear]] and only had a residual [[anti-submarine warfare|anti-submarine ability]] while the Bs were equipped with Type 119 [[ASDIC]] (sonar) and had a full complement of [[depth charge]]s, but could not use the TSDS. This was the beginning of the [[British Admiralty|Admiralty]]'s policy of alternating TSDS and anti-submarine capabilities between destroyer flotillas.<ref>Lenton, pp. 150–152</ref> The ships displaced {{convert|1350|-|1360|LT|t|lk=on}} at [[Displacement (ship)|standard]] load and {{convert|1778|-|1790|LT|t}} at [[deep load]]. They had an [[length overall|overall length]] of {{convert|323|ft|m|1}}, a [[beam (nautical)|beam]] of {{convert|32|ft|3|in|m|1}} and a [[draft (hull)|draught]] of {{convert|12|ft|3|in|m|1}}.<ref name=w78>Whitley, pp. 97, 99</ref> The A class had a [[metacentric height]] of {{convert|1.76|ft}} at deep load.<ref>March, p. 256</ref> The ships' complement was 138 officers and [[naval rating|ratings]] as built,<ref name=l0/> but increased in size up to 162 during the war.<ref>March, p. 258</ref>

The destroyers were powered by two [[Parsons Marine Steam Turbine Company|Parsons]] geared [[steam turbine]]s, each driving one [[propeller shaft]] using steam provided by three [[water-tube boiler]]s equipped with [[superheater]]s. Five of the As and all of the Bs had [[Admiralty three-drum boiler]]s that operated at a pressure of {{convert|300|psi|kPa kg/cm2|0|lk=on}} and a temperature of {{convert|600|°F}} while ''Ardent'' and ''Anthony'' were fitted with [[Yarrow boiler]]s of {{convert|275|psi|kPa kg/cm2|0|abbr=on}} pressure at the same temperature. ''Acheron'' was given experimental [[Thornycroft boiler]]s that had a working pressure of {{convert|500|psi|kPa kg/cm2|0|abbr=on}} and a temperature of {{convert|750|°F}} to examine the weight and economy savings.<ref name="WPCleanerAuto1">Friedman, p. 198</ref> Her specific fuel consumption was reduced from {{convert|0.8|lb|abbr=on}}/[[horsepower|hp]]/hour in her sisters to {{convert|0.6|lb|abbr=on}}/hp/hour,<ref>Lenton, p. 151</ref> although she was plagued by mechanical problems for her whole life.<ref name="WPCleanerAuto2">English, p. 19</ref> In the event the trials were inconclusive, and the Admiralty continued to use the lower-temperature and pressure Admiralty three-drum boiler until the {{sclass2|Battle|destroyer|4}} of 1942, nearly ten years after other major navies began to use higher-pressure and temperature boilers.<ref>Rippon, pp. 241–245</ref> The turbines developed a total of {{convert|34000|shp|lk=on}} for a designed speed of {{convert|35|kn}} and the ship exceeded that during their [[sea trial]]s.<ref>March, pp. 247, 260</ref> The destroyers carried a maximum of {{convert|388|-|390|LT|t}} of [[fuel oil]] that gave them a range of {{convert|4800|nmi|lk=in}} at {{convert|15|kn}}.<ref name=l0>Lenton, p. 152</ref>

All of the ships had the same main armament, four [[List of British ordnance terms#QF|quick-firing (QF)]] [[4.7 inch QF Mark IX & XII|{{convert|4.7|in|mm|adj=on}} Mark IX]] guns in single mounts with enlarged [[gun shield]]s, 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°.<ref>March, pp. 247, 250, 252, 260</ref> They fired a {{convert|50|lb|kg|adj=on}} shell at a [[muzzle velocity]] of {{convert|2650|ft/s|m/s|abbr=on}} to a range of {{convert|16970|yd|m}}.<ref>Campbell, p. 48</ref> Each gun was provided with 190 [[Cartridge (firearms)|rounds]]. For [[Anti-aircraft warfare|anti-aircraft]] (AA) defence, the A- and B-class ships carried two {{convert|40|mm|adj=on|1}} [[QF 2 pounder naval gun|QF two-pounder Mark II]] AA guns mounted on platforms between the [[funnel (ship)|funnel]]s, each with 500 rounds. They were fitted with two quadruple mounts for [[British 21-inch torpedo|21-inch (533&nbsp;mm)]] [[torpedo tube]]s.<ref name="WPCleanerAuto1" /> 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.<ref>Friedman, p. 197</ref> The Bs were equipped with two throwers and one rack for twenty depth charges.<ref>March, p. 260</ref> 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.<ref>English, pp. 17, 19, 24</ref>

The [[Ship gun fire-control system|fire-control system]] for these ships was little advanced over their First World War-era predecessors. A pedestal-mounted, manually operated Destroyer [[Director (military)|Director]] Sight and a separate {{convert|9|ft|adj=on|spell=in}} [[Rangefinding telemeter|rangefinder]] positioned to its rear were situated above the [[bridge (nautical)|bridge]]; the director transmitted training angles and firing impulses to the main guns, which fired at fixed elevations.<ref>[http://dreadnoughtproject.org/tfs/index.php/British_Destroyer_Director_Firing_System#Director The Dreadnought Project page on the British Destroyer Director of WW1]</ref> 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 and D-class destroyer|C-class destroyers]].<ref>Campbell, p. 14; Friedman, p. 207; Hodges & Friedman, p. 10</ref>

===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 (ship)|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 {{convert|3|ft|m|1|spell=in}} shorter than their British counterparts. Although the ships had an additional {{convert|50|LT|t}} of fuel, {{convert|2000|shp|abbr=on}} 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 {{convert|1337|LT|t}} at standard load and {{convert|1805|LT|t}} 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.<ref>English, p. 26; Lenton, pp. 153–154</ref>

===Flotilla leaders===
{{HMS|Codrington|D65|2}} 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 {{convert|200|LT|t}} more than the [[private ship]]s ({{convert|1540|LT|t}} at standard load and {{convert|2012|LT|t}} at deep load); she was {{convert|20|ft|m|1}} longer overall and had a beam {{convert|1|ft|m|1}} wider. She shipped a fifth 4.7-inch gun between the funnels, which forced the two-pounders to be repositioned [[abaft]] the rear funnel,<ref name=l0/> and was not fitted with TSDS. To compensate for her greater size, ''Codrington''{{'}}s oil tanks were increased by {{convert|40|LT|t}} and her turbines were rated at {{convert|39000|shp|abbr=on}} to give her the same range and speed as the private ships, but she proved to be significantly faster as she made {{convert|37.7|kn}} 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.<ref>March, pp. 247, 258–259</ref>

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.<ref>Friedman, p. 205; March, pp. 265, 267, Whitley, p. 99</ref> ''Keith'' was {{convert|40|LT|t}} heavier than the private ships at standard load and nearly {{convert|100|LT|t}} heavier at full load ({{convert|1400|LT|t}} and {{convert|1821|LT|t}}, respectively) and carried 19 additional officers and ratings.<ref name=l0/>

===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 3 inch 20 cwt gun|QF {{convert|3|in|mm|spell=in|adj=on}} 20-cwt anti-aircraft gun]],<ref group=Note>"Cwt" is the abbreviation for [[hundredweight]], 20 cwt referring to the weight of the gun.</ref> the after mast and funnel being cut down to improve the gun's field of fire.<ref>Friedman, pp. 233–236, 239, 241</ref> Of the early war losses, only ''Codrington'' and ''Acheron'' received this modification before they were sunk.<ref>Whitley, p. 97</ref><ref name="WPCleanerAuto2" /> 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.<ref>Friedman, p. 241</ref>

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 [[Oerlikon 20 mm cannon|QF Oerlikon {{convert|20|mm|adj=on}} guns]], one each abreast the bridge, and a [[Type 286 radar|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 [[Vickers .50 machine gun|{{convert|0.5|in|mm|adj=on|1}} machine guns]] and were not fitted with Oerlikons by 1942.<ref>Friedman, pp. 237, 242, 245; Lenton, pp. 152, 154</ref>

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 (weapon)|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 radar|Type 271]] target-indication radar. ''Beagle'' and ''Bulldog'' were later fitted with a two-pounder [[bow chaser]] to engage German [[E-boat]]s in the [[English Channel]] while ''Boadicea'' received two elderly six-pounder (57&nbsp;mm) [[Hotchkiss gun]]s to deal with U-boats on the surface at close range.<ref>Friedman, pp. 247, 252–253</ref>

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&nbsp;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.<ref>Friedman, pp. 242–247</ref>