The Royal Navy ordered the first four ships in 1938, with a further two acquired as part of the War Emergency Programme. They were specifically designed for the rapid laying of minefields in enemy waters, close to harbours or sea lanes. As such they were required to be very fast and to possess sufficient anti-aircraft weaponry to defend themselves if discovered by enemy aircraft.
A large mineload of up to 150 mines was required to be carried under cover, therefore a long, flushdecked hull with high freeboard was required. The mines were laid through doors in their sterns; the ships carried their own cranes for loading.
In size these ships were almost as long as a cruiser, but laid out much like a large destroyer. However, the three straight funnels were an instant identifying feature. Top speed was specified as 40 knots (74 km/h). To achieve this they were given a full cruiser set of machinery and with an installed output of 72,000 shaft horsepower (54,000 kW) on two shafts, they made 39.75 knots (73.62 km/h) light and 38 knots (70 km/h) deep load. To put this into perspective, the contemporary Town-class cruisers had 80,000 shp (60,000 kW) and a full load displacement of 12,980 tons, just short of four times that of the Abdiels.
The ships were initially to be armed much as destroyers, with three twin CP Mark XIX mounts for the QF 4.7-inch (120 mm) Mark XII gun (which had a maximum elevation of only 40°) in 'A', 'B' and 'X' positions, a quadruple "multiple pom-pom" mounting Mark VIII for the QF 2-pounder Mark VIII and a pair of quadruple 0.5 inch Vickers machine guns.
Wartime modifications involved adding a Type 279 Radar at the masthead, a primitive metric wavelength air warning set, later replaced by a Type 286 then a Type 291, as they became available. A Type 285 Radar was fitted to the rangefinder-director on the bridge, this was a metric set and could provide target ranging and bearing information. The centimetric Type 272, a target indication radar with plan position indicator (PPI), was fitted to the front leg of the foremast. Following the loss of Latona to air attack, the surviving ships were re-armed with three twin HA/LA Mark XIX mounts for the QF 4-inch (100 mm) L/45 Mark XIV gun with an elevation of 70° to remedy the shortcomings in anti-aircraft defence. Those on the stocks were armed with these mountings from new, but 'B' mount was suppressed and replaced (in Ariadne only) by a twin Mark IV "Hazemeyer" mounting for the 40 mm Bofors. Both Ariadne and Apollo had two such mountings sited amidships, replacing the pom-pom in 'Q' position, and these mounts carried their own Type 282 Radar for target ranging. Six single 20 mm Oerlikon guns were initially added on P Mark III pedestal mountings, although these were later replaced by powered twin Mark V mountings. In 1945 Ariadne was refitted in the United States in July 1945 for far eastern service, when the Bofors mounts were replaced by American pattern models (Mark I) with off-mounting "simple tachymetric directors" (STD) fitted with Type 282 Radar and the Oerlikon mounts regunned with Bofors guns (this combination was known as the "Boffin").