Before escaping, Walenn had given Cassie his gold watch, a 21st-birthday
present from his parents. After the war, Cassie fulfilled a promise he had
made to his friend and returned it to them.

In the tragic aftermath of the break out, escape activities were reduced, but
X-Organisation continued to operate and Cassie took over the running of Dean
Dawson. In the event, no further attempts to escape were made. In
September, after the Nazis posted an order declaring that “escape from
prison camps is no longer a sport”, PoWs were informed via underground
contacts with MI9 that escapes should not be risked.

With the Soviet Army advancing from the east, the Germans emptied the PoW
camps in Poland in late January 1945, and Cassie and fellow prisoners were
forced to march westwards in what later became known as “The Long March”.
They were eventually liberated by the British Army in April.

The son of Scottish parents who emigrated to South Africa, Alexander “Sandy”
Cassie was born on December 22 1916 in Cape Province and educated there at
Queenstown School.

He returned to Scotland to study at Aberdeen University, where he graduated in
1938 with a degree in Psychology. For a year he worked in Peterhead on a
time and motion study in a personnel department before joining the RAF to
train as a pilot.

Cassie joined No 77, Squadron which was equipped with the ageing Whitley
bomber. He flew operations over France and Germany but, with the Battle of
the Atlantic intensifying, a number of Bomber Command squadrons were loaned
to Coastal Command. These included No 77, which deployed in May 1942 to
Chivenor in Devon for patrols over the Bay of Biscay.

During the early hours of September 2 1942, Cassie took off for a strike
operation against enemy shipping. He discovered the German submarine U-256
on the surface and attacked at very low level, dropping his armour-piercing
bombs just astern and damaging the vessel. However, the Whitley had been hit
by return anti-aircraft fire, disabling one of its engines. Unable to
maintain altitude, Cassie had to ditch. A Cornish airfield had picked up a
faint SOS but it soon faded and the crew were posted as missing.

Cassie and his four colleagues were quickly picked up by a French fishing boat
which landed them at Concarneau in southern Brittany – where the Germans
were waiting. A few weeks later, Cassie arrived at Stalag Luft III.

After his release from the RAF as a flight lieutenant at the end of the war,
Cassie joined the Civil Service as a psychologist. For many years he worked
in the Air Ministry developing psychometric tests for potential aircrew who
attended the RAF’s officer and aircrew selection centre. Following numerous
promotions, he moved to the Army Personnel Research Establishment in
Farnborough, developing and overseeing exercises and tasks for potential
candidates attending the Army’s Regular Commissions Board at Westbury. He
retired in 1976 as a senior principal psychologist. He was elected a Fellow
of the Royal Psychological Society.

Cassie’s passion for art remained with him and he painted in various mediums
until a few years before his death. He won several awards for his animated
films, and triumphed at an annual competition sponsored by the magazine
Amateur Movie Maker. One of his successful exhibits was an animation based
on Picasso’s Three Musicians.

Alexander Cassie married Jean Stone in December 1949. She died in 2005 and he
is survived by their son and daughter.

Alexander Cassie, born December 22 1916, died April 5 2012