There are two answers here that are clearly off beam: James Dyson was the inventor and developer of several consumer products; Christopher Cockerell was the inventor of the hovercraft. What of the other two names?

Experiments with ejection seats date back to the first half of the 20th century. The modern design owes its existence to a company now known as Martin-Baker Aircraft Co. Ltd. but which was founded in 1934 by James Martin (1893-1981) and Valentine Baker (1888-1942) as "Martin's Aircraft Works". Martin-Baker ejection seats are now used throughout the world.

The two-man team did not start with ejection seats, but with aircraft. They developed several designs during World War II, none of which was widely adopted. Martin-Baker had investigated ejection seats from 1934 onwards, years before Germany and Sweden proposed similar systems in 1938. But it was only after the war that the company fully focused on ejection seats rather than aircraft.

There were two factors behind this reorientation. First, in 1944, James Martin was asked by the Ministry of Aircraft Production to develop methods for fighter pilots to escape their aircraft. Second, Baker's death in 1942 during a test flight of one of their aircraft affected Martin so much that pilot safety became his primary focus.

Martin was the inventor of the aircraft and also the ejection seats. Baker, the test pilot, never lived to see the famous ejection seats but his name is commemorated in the company.

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