pics and caption via Apostles of Mercy Blog.
The Armstrong Whitworth AW.681, also designated the Whitworth Gloster 681 or Hawker Siddeley HS.681 - due to industry mergers - was a pretty unique transport design from Britain’s 1960s aviation industry. Fulfilling a similar short takeoff and landing specification as Lockheed’s C-130, Armstrong Whitworth produced a solid contender in the AW.681, featuring vectored thrust nozzles, boundary layer control, blown flaps, leading edges and ailerons.
Then they took things a little further, trading the four Rolls-Royce RB.142 Medway engines for four Bristol Siddeley Pegasus turbofans, to obtain VTOL capability. These were the engines which went on to power the Harrier. It would have been an interesting sight. Thanks to the swept shoulder-mounted wings and high T-tail, it would have also resembled today’s C-17 and A400M.
The entire project was scrapped in 1964 when the moment’s Labour Government announced a defence spending review, opting instead to buy the American Lockheed C-130. As a result the company closed it’s Coventry factory, making 5000 redundant.