The ships were modified throughout their wartime service, particularly their anti-aircraft (AA) guns; they were also fitted with radar.

In a departure from all previous Royal Navy destroyers, the design used a two boiler room layout.

As destroyers are lightly armoured and fast vessels meant to survive by avoiding being hit at all, the odds of a single hit striking just the right spot to disable both boiler rooms simultaneously were considered remote enough to be worth risking in exchange for the benefits given by a two-room layout.

"[1] A significant advancement in construction techniques was developed by naval architect Albert Percy Cole.

The armament was based on that of the Tribals, but replaced one twin QF 4.7-inch (120 mm) Mark XII (L/45) gun mount with an additional bank of torpedo tubes.

The only design change was to locate the 'X' 4.7-inch mounting in the more logical position with the 20° training blindspot forward.

While building, the same early wartime modifications as the Js and Ks were applied, with a pair of twin power-operated 0.5 in machine gun turrets briefly carried on the quarterdeck before being replaced by single 20 mm Oerlikons.

The relatively ineffective multiple 0.5-inch machine guns were replaced with a single 20 mm Oerlikon, with a further pair added abreast the searchlight platform amidships.

Being amongst the Royal Navy's most modern and powerful destroyers at the outbreak of war, they were extensively committed.