A light carrier of the Colossus class, the most numerous class of light aircraft carriers in the Royal Navy. Theseus occupies an intermediate position between the Illustrious-class heavy carriers and escort carriers. To reduce costs and expedite construction, technologies used in building merchant ships were employed. Theseus actively participated in the Korean War as part of the UN forces. Later, she was refitted for service in Training Squadron, Home Fleet, before being placed in reserve in 1956.