Common to all three ships was a traditional rivetted hull, steel flight decks and a closed hangar. They had the same propulsion provided by diesel engines connected to two shafts giving 11,000 brake horsepower (BHP), which could propel the ship at . Their armaments concentrated on anti-aircraft (AA) defence and comprised two 4 inch Dual Purpose, AA guns on a twin mount, sixteen 20 mm anti-aircraft cannons on eight twin mounts and sixteen 2 Pounder Pom Pom on four quadruple mounts. Aircraft assigned were either anti-submarine or fighter aircraft, which could be made up of a mixture of the Hawker Sea Hurricane, Grumman Wildcat, Fairey Fulmar or Fairey Swordfish. The exact composition of the embarked squadrons depended upon the mission. Some squadrons were composite squadrons for convoy defence and would be equipped with anti-submarine and fighter aircraft, while other squadrons working in a strike carrier role would only be equipped with fighter aircraft.