Status: tested 1933.
Ridge never flew in it, but English pilots broke two world aircraft altitude records with a derivative of the suit in 1935-1936.
Dr John S Haldane, a physiologist, worked with Sir Robert Davis of Siebe, Gorman and Company, London, on development of deep sea diving suits. In the 1920's Haldane made the first documented suggestion that a suit resembling that of deep sea divers could be used to protect pilots at high altitudes. Meanwhile American daredevil Mark Edward Ridge realized he needed such a suit in order to make his planned expedition into the stratosphere by balloon.
Unable to interest the US military (which was in a race with the Soviet Union to set manned balloon altitude records using pressurized gondolas), Ridge collaborated with Haldane and Davis. They fabricated a hypobaric protection suit for Ridge by substantially altering one of their diving suits. In November 1933 the suit was tested in Haldane's pressure chamber up to simulated altitudes of up to 25.6 km (the suit remaining pressurized to 11.1 km equivalent altitude). He brought the suit back to the United States, but almost killed himself demonstrating it at a dry ice factory in May 1934. Ridge himself was never able to obtain backing for his balloon concept. He was finally judged insane in 1942 and never saw the outside of an asylum until his death in 1956.
A second suit, based on the Ridge-Haldane-Davis design, was built for the Royal Air Force and flown to a British altitude record of 15,226 m by Squadron Leader F. R. D. Ferdie Swain in the autumn of 1936. However Swain nearly suffocated, and only saved his life by slicing open his helmet with a knife just as he was losing consciousness.