In 1941, whilst serving with the British Royal Air Force, he stole a fighter aircraft from England, and flew it to Occupied Europe where he surrendered it to the German authorities.

He was subsequently freed and sent on an espionage mission with orders to join the emigre Czechoslovak military diaspora that was fleeing their country after its occupation to Western Europe, particularly seeking to fall into the company of any groups of air force personnel, and report back to Germany on their activities.

[1] After a brief period in Poland, Přeučil, in company with a group of nearly 200 other Czechoslovak military personnel, travelled to France in August 1939 intending to enlist with the French Army's Foreign Legion.

Whilst engaged in the manoeuvres Přeučil reported over the radio that his aircraft was out of control, and breaking away into the clouds, flew the aeroplane to Occupied Europe, landing in the countryside near Bastogne, Belgium.

[3] In September 1941, having been debriefed by the Abwehr with all the information about the British military that he had to give, and been generously financially rewarded for his actions, Přeučil returned to Protectorate of Bohemia and Moravia, and for the remainder of the war he acted as an undercover agent for the Gestapo there, infiltrating and betraying Czech Resistance movements.

In 1944 he was reportedly working for the Gestapo in Prague, and assisted the Wehrmacht in interrogating captured Czech and Polish Royal Air Force aircrews who had been shot down over occupied Europe.

After two years of investigation he was tried by Chief Public Prosecutor Jaroslav Drábek on 3 March 1947 on charges of High Treason against Czechoslovakia, found guilty and sentenced to death.