The "real" Unicorn was a lightweight (15,000 tons) carrier that was not intended for flying off aircraft into battle, but as a maintenance carrier with appropriate materials and shops on hand to serve the Fleet carriers. Out of desperation, she was used in the Salerno operation to fly off Spitfires (in VTS, is an   0   2   3 ¹) , but was used thereafter only for servicing other CV's aircraft.

In "Grand Fleet" the Royal Navy feels it needs a carrier that is not so "timid" and thin-skinned as to veer away from battle, and could ward off   8" shell hits or 1,000 lb bombs and still keep operating aircraft. With the lapse of the Washington Treaty in 1936 that effectively kept carrier tonnage at 27,000 tons or less, Britain looked to see just what could be done to effectively armor a carrier.

The Unicorn represented the extreme of the armored carrier concept. Accepting the penalty of a small complement of aircraft, the Unicorn used a huge, elongated "horseshoe" of armor, nearly her whole length, to protect both her vitals and aircraft. Like a "C" on its side with the open end facing the keel, the armor was 11" thick on the sides (belt), 8" thick on the shoulders, and 5 1/2 inches on top. The back of the "C" formed the center portion of the flight deck, taking up half the actual width (the rest of the flight deck was steel plate, but "expendable" as long as the center portion held). Two armored lifts, with massive machinery to elevate and lower them, fit tightly into the lift wells and formed the only breaks in the armored shield. The lifts were very fast, minimizing the time that a gap appeared. Theoretically, aircraft could be readied and fueled below, then raised to the flight deck "in between salvoes" without jeopardizing protection for others below. This incredible heaviness so high in the ship was offset by a deep draft, very low freeboard, and by a huge pool of liquid mercury directly over the keel. In the event of a list, liquid-filled voids normally used as anti-torpedo blisters could be flooded by mercury pumped into them, displacing the lighter fluid on the opposite side to correct the list.

She fought in the North Sea and the Mediterranean with the "battlecreepers", once operating aircraft while being accurately shelled by an Italian heavy cruiser. She operated biplane Fairey Albacore aircraft that could get airborne, fully loaded, without a long take-off run (given the inability of Unicorn to produce high winds over the deck due to her slow speed). Even the eccentric British recognized Unicorn as a nice experiment, but a mistake, and in late 1944 her armor was removed and she became a maintenance CV for operations in the Far East.