He inherited a love of flight from his father, who had served with the Royal Flying Corps in the First World War, and drew aircraft as a child.

Walenn had connections to the East Finchley and Golders Green areas[3] when he enlisted in the Royal Air Force Volunteer Reserve in 1937 as a trainee pilot.

25 Operational Training Unit, Walenn took off in a Wellington Mark Ic bomber (serial number N2805) from RAF Finningley at 1955 hours on the night of 10 September 1941[11] to bomb the Misson ranges.

Walenn was captured and sent to Stalag Luft III in the province of Lower Silesia near the town of Sagan (now Żagań in Poland).

He became a well-known character in the prison camp system for his skilful drawing, as well as for his enormous handlebar moustache[12][13] which had to be shaved off for the escape due to its unmistakable RAF style.

[15] His team produced forged passports, movement orders, railway documentation and all manner of identity papers to move about Germany.

Travelling in a group of four escapees with Gordon Brettell, Romualdas Marcinkus and Henri Picard, all posing as French and Lithuanian workers, they managed to reach a train heading towards Danzig (now Gdansk, Poland).

The four were taken to Stalag XX-B and spent the night there, their presence being carefully recorded by the camp sergeant-major, who issued them with clothing more suited to prisoners of war in the hope of avoiding the possibility of them being charged with espionage.