For the first thirty years of carrier aviation, landing on a ship worked like this. You flew a curving approach towards a straight deck with aircraft parked on the front half of it. A man standing on the stern waved coloured paddles at you. If you got it wrong and missed the wires, a steel barrier stopped you before you reached the parked aeroplanes, usually by destroying yours.

Then jets arrived, heavier and faster, with engines that took several seconds to spool up. The old method stopped working. Two British officers fixed it within four years of each other, and every carrier afloat today still uses both of their ideas.

The idea that got a mixture of apathy and mild derision

Cambell was in his office at the Ministry of Supply, preparing for a meeting, looking at a three-foot model of HMS Illustrious and trying to work out how to lay out a deck that could handle jets. His own account of what happened next is refreshingly free of false modesty.

Rotate the landing area a few degrees away from the ship’s centreline and the entire problem dissolves. The landing run no longer points at the parked aircraft, so the barrier becomes unnecessary. An aircraft that misses the wires simply flies off the angled deck and goes around, which is where the word bolter comes from. And because the forward deck is no longer in the landing path, the ship can launch and recover at the same time instead of alternating between the two.

The meeting was not impressed.

He recorded the reaction as a mixture of apathy and mild derision. One man in the room did not dismiss it: Lewis Boddington, a civilian technical officer from RAE Farnborough, asked to look at the sketch afterwards and began refining it. Weeks later Boddington proposed applying the angled deck to the design of HMS Ark Royal, and the idea started moving.

The Smithsonian Channel on why angling the deck changed carrier aviation permanently.

The second idea: stop trusting the man with the paddles

The angled deck solved where you landed. It did not solve how you arrived there. That was Nicholas Goodhart’s problem, and in 1951 he produced the mirror landing sight.

The principle is beautifully simple. A bright source light is shone into a concave mirror mounted beside the landing area, angled to project a beam of light up the correct glideslope. The pilot sees a spot of light, the ball, reflected in the mirror. Beside it sits a horizontal row of green datum lights. If the ball is above the datums, the aircraft is high. Below, low. Level with them, on glideslope.

The genius is what it removes. The old system depended on a human being on the deck judging another human being’s approach and signalling corrections, with all the lag that implies. The mirror gives the pilot the information directly, instantly, from his own cockpit. It does not interpret. It simply tells him where he is.

Mirrors gave way to Fresnel lenses, which are more compact and more precise, and the modern Improved Fresnel Lens Optical Landing System is gyroscopically stabilised so that the projected glideslope stays where it should be while the ship moves underneath it. That stabilisation matters more than any other refinement. A deck in a swell can move many feet vertically, and an unstabilised glideslope would move with it.

What the meatball actually is, and how a pilot reads it.

Why the LSO is still there

If the optical system tells the pilot everything, why does the US Navy still put experienced aviators on a platform at the back of the ship in the weather?

Because the ball tells a pilot where he is, not where he is going. An LSO watching an approach can see a rate of change the pilot cannot yet feel, hears the engine, knows the aircraft type, knows this particular pilot’s tendencies, and can say the one word that fixes it. They also grade every single pass, which is the mechanism by which carrier aviation keeps its standards from drifting. A naval aviator’s landing grades are public within the squadron and taken extremely seriously.

So the answer is that neither invention replaced the human. The angled deck removed the consequences of a bad approach. The mirror removed the guesswork from a good one. The LSO remains for the part that is still judgement.

From the LSO platform aboard USS Ronald Reagan, where recoveries are watched and graded.

Sources: denniscambell.org.uk for Captain Cambell’s own account; Wikipedia for the angled flight deck and optical landing system chronologies; US Navy imagery.