Editing A- and B-class destroyer (section)

===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>