At the defeat of Poland in September 1939, he was given the responsibility of ferrying the presidential papers in a small plane to Romania, then escaped to France and England where he flew in a Polish bomber squadron in the Royal Air Force.
In 1943 he obtained a scholarship to study for a master's degree in aeronautical engineering at Imperial College, London, joining Airspeed Ltd. in 1945 and later the Percival Aircraft Company.
With two colleagues, Gordon Bennett (head of structures) and James Tutty,[3] he entered a design competition sponsored by the Royal Aero Club of London for a replacement aircraft for the de Havilland Chipmunk.
Millicer also had developed a slightly larger 4 place aircraft known as the Aircruiser, with one prototype built at the Bankstown, New South Wales, Victa factory and first flown in 1966.
Millicer became the principal lecturer in Aeronautics at the Royal Melbourne Institute of Technology (RMIT) with a view to establishing this faculty as the leading school in Australia.