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. The hull-mounted sponsons were used rather than wing tip 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 A.33 serial numberK4773 first flew on 14 October 1938. Unfortunately, the A33 prototype 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.