[2] Czernin returned to the United Kingdom in April 1935 to take up an appointment as an acting pilot officer on a short service commission in the Royal Air Force (RAF).
On 16 May Czernin had to walk back to his squadron at Lille Airport after force-landing his aircraft, damaged by a Messerschmitt Bf 109 of 3/JG76.
17 Squadron, Czernin fought with distinction throughout the Battle of Britain, tallying a Do 17 of II/KG2 on 12 July (shared), which crashed into the sea near a convoy off Orfordness.
In May 1941 he was posted to an Operational Training Unit at RAF Debden and promoted to acting squadron leader in December.
28 Group, RAF Uxbridge, until he was recruited by Special Operations Executive (SOE) under the cover of another similar assignment.
Czernin was parachuted into northern Italy, not far from the Austrian border, on the night of 13 June 1944, winning in the process a Military Cross for his decision to go ahead with the jump in spite of dubious signalling from the "welcome party" on the ground: it was not infrequent for the Germans to try to intercept Allied airdrops to get hold of both of men and supplies directed to the Italian Resistance.
His second mission took place in March 1945 when he parachuted in Lombardy, taking command of the operations that led to the surrender of Bergamo.
"[5] His citation for the Military Cross reads: On the night of 12–13 June 1944, Squadron Leader Czernin and his Wireless operator were to be dropped into enemy-occupied territory, but the reception signals were not satisfactory and they returned to base.
This he did without arms of any description and with the full knowledge that the Germans are constantly arranging bogus receptions for the receipt of Allied personnel and stores.
But for this courageous action, a most vital operation would have had to be postponed at a stage when the time was of the utmost importance to the success of the major plan.
To reach the Bergamasco area he had to cross the 9,000 ft (2,700 m) Passo del Diavolo which was six feet deep in snow.
The DSO citation said that he "displayed the highest qualities of leadership and by his courage and daring made a notable contribution to the Allied success in North Italy.