On graduating in 1943, Park turned down jobs in the Treasury and the Foreign Office to make a direct contribution to the war effort. She then joined the First Aid Nursing Yeomanry (FANY). During the selection process for FANY, she came to the attention of the Special Operations Executive (SOE), due to her understanding of ciphers. Park was promoted to the rank of sergeant and trained groups of operatives for Operation Jedburgh, whose task was to support the Resistance in Europe. In 1945 Park went to work as a briefing and dispatching officer in North Africa. On her return in 1946 she was sent to Vienna to establish an office for the Field Intelligence Agency Technical (FIAT), a unit of the Allied Commission responsible for tracking down former Axis scientists.