Following the period of the "Phoney War", the Wehrmacht's attack and breakthrough in the Ardennes in May 1940 succeeded in splitting the Allied Armies, and surrounding the French 1st Army and BEF, Gort took the unilateral decision to abandon his orders received from the British Government for a southward attack to be made to support the French Army, instead on 25 May 1940 ordering a retreat by the BEF northwards to the French coast. On reaching the coast Gort oversaw the en masse retirement of the BEF back to the British Isles, involving the Battle of Dunkirk and the Dunkirk evacuation, while France was defeated and surrendered to the armies of the Third Reich four weeks later.