The D.521 (Great Britain) is a gift British fighter. It was introduced in the game during the Open Beta session as a reward vehicle for the June 2013 "Vive la Liberté!" video contest and again for the 2014 "First Flight of Dewoitine D.520" event. The D.521 was a modified variant of the French Dewoitine D.520 which featured a Rolls Royce Merlin III engine and slight armament changes. Only one model was ever produced.

The D.521 is essentially a slightly improved version of the D.520. It has a somewhat improved engine (Rolls-Royce Merlin III) which constitutes the one major change. It does however have a slightly worse turn and climb rate which may be due to the added weight of said engine. At either rate, tactically, it is advised that you have good knowledge of the various aircraft's you will face as it does not excel at any one thing. By applying situational awareness and a degree of caution to your approach, you may find yourself to be quite successful with this machine, but regardless of if you approach this in Arcade or Realistic battles, you need to have a good idea about the aircraft you are likely to face in the battle rating of this aircraft.