In 1937 Hargrave became obsessed with solving the technological problems of using maps in moving aeroplanes. By 1938 a prototype of the Hargrave Automatic Navigator was ready to file with the Patent Office and articles of association had been prepared for 'Hargrave Aviation Ltd.'. The prototype was tested during the war, with government approval, but lack of capital meant that the invention was not developed further. The invention lay fallow until 1976 when Hargrave sued the British Government, claiming that the moving map display supplied by Britain to the supersonic Concorde, was, in fact, his Automatic Navigator. His claim was taken up by journalists, resulting eventually in a Public Enquiry. Hargrave insisted he was only asking for recognition, rather than any financial recompense, but the Public Enquiry found against him.