[citation needed] After officer training at the Royal Military College, Sandhurst, Hansen was commissioned into the Lincolnshire Regiment on 4 March 1911.

[2] Hansen was appointed as a temporary captain shortly after the outbreak of war in 1914, as adjutant in the 6th (Service) Battalion of the Lincolnshire Regiment,[1] and his promotion was made permanent in the following April.

Hansen and volunteers repeatedly moved back and forth under heavy fire to successfully rescue six wounded men from capture, or death by burning.

His next assignment was as a General Staff Officer Grade 2 (GSO2) to the 55th (West Lancashire) Division, a Territorial Army (TA) formation, and then a GSO2 in Jamaica, before returning to the United Kingdom and being made Deputy Assistant Adjutant-General (DAAG) with Western Command.

[1] On 2 September 1939, the day before the war began, Hansen was posted to the 55th (West Lancashire) Infantry Division, a TA formation which he had served with before, and was made Assistant Adjutant-General & Quartermaster-General (AA&QMG).

He held this post until late January 1941, when he became Deputy Assistant & Quartermaster-General (DA&QMG) with XII Corps, then commanded by Lieutenant General Andrew Thorne.

The corps, which was commanded from late April by Lieutenant General Bernard Montgomery, had responsibility for the defence of Kent in the event of a German invasion of the United Kingdom.