Why do aircraft carriers have angled decks?

Early carriers had a single axial deck: aircraft landed at the stern and rolled toward the bow, where the machines that had already landed were parked behind a wire crash barrier. If a pilot caught no arresting wire, that barrier was the only thing between him and the deck park. Faster, heavier jets made this worse: approach speeds rose, the barrier stopped them brutally and a missed wire could end in a fatal pile-up. Launching and recovering at the same time was impossible, because the bow catapults sat exactly where the landing roll ended.

Captain Dennis Cambell of the Royal Navy proposed in 1951 painting the landing strip at an angle to the ship's centreline. HMS Triumph tried the layout with painted markings in 1952, and the US Navy tested it on USS Antietam in 1952-1953 before adopting it for the new Forrestal class and refitting Essex-class ships. The offset, roughly 9 to 10 degrees to port, is small enough to keep the landing run within the hull and large enough to point a go-around over open water.

The angled section carries the arresting gear and the optical landing aids; the bow keeps the catapults. A pilot now applies full power the instant the wheels touch, so that a missed wire, a bolter, simply becomes a climb. Recovery can proceed while the bow launches, which raises sortie rates and shortens the vulnerable phase of each cycle. The layout also frees a large parking area to starboard, ahead of the island, that interferes with neither operation. Ski-jump carriers flying STOVL aircraft do not need the angle, because their jets land vertically; every catapult ship, from the Nimitz and Ford classes to Charles de Gaulle, keeps it.