RPE were not the only people to look at liquid hydrogen: both Bristol Siddeley and Rolls Royce were interested. These two firms were merged under Government pressure in the early 60s.
Work was carried out for a liquid hydrogen under an ELDO contract, although funds were very limited. It would have been used in the upper stages of the ELDO B and C launchers, proposed by the French in 1964, but never proceeded with. In the ned, Rolls Royce test fired the motor using its own funds.
This is an impression of the Rolls Royce RZ20 engine.
And this is an outline drawing of the motor:
One of two test firings of the RZ-20 at Spadeadam:
photograph courtesy of the Science Museum.
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