The A.33 was a four-engined flying-boat with a parasol monospar wing, the wing was supported by two angled N-struts which connected the wing to hull-mounted sponsons. Hull-mounted sponsons were used rather than wingtip floats and were also used as fuel tanks. A Saro Cloud was modified with a monospar wing and sponsons to test the design concepts. The prototype A.33 United [Kingdommilitary aircraft serials|serial number] K4773 first flew on 14October 1938. However, it was written off after structural failure sustained during high-speed taxi trials on 25 October 1938 and development was abandoned. A production contract for eleven aircraft was cancelled.