I remember hearing Dick Stratton (ex-Saunders Roe) talking about the SR53. Apparently a Javelin went into a deep stall and crashed on the Isle of Wight in the late 50s. Maurice Brennan, the SR53 designer, was held up in the resultant traffic jam, and went into the Cowes works the next day saying they had to put an anti-stall device on the SR53. If they were flying the SR53 then this dates it to 1957-59. As far as I can remember, this was some sort of pyrotechnic designed to lift the tail in the event of such a stall.