Commissioned into the Seaforth Highlanders as a lieutenant on 6 June 1939, Chapman was chosen for a mission in Australia to train Australian and New Zealand forces in guerrilla warfare and eventually to join what was then Special Training School 101 STS-101 in Singapore.
Commissioned into the Seaforth Highlanders as a lieutenant on 6 June 1939, Chapman's love of the outdoor life and adventure lead to him being chosen for a mission in Australia. That mission was to train Australian and New Zealand forces in guerrilla warfare and eventually to join what was then Special Training School 101 STS-101 in Singapore.