Lord Lovat first enlisted in the Scots Guards in 1932, leaving the army in 1937. Two years later at the outbreak of war he rejoined the Army in the Lovat Scouts.

Lord Lovat was part of a small but elite group of men who formed the idea of a Special Training Centre, agreed on the location, and devised and implemented a course of training once it was approved. This became the first of many Special Training Centres, STC Lochailort.

The training took place in and around the camp at Lochailort, Lord Lovat's role being Fieldcraft instruction.

After being appointed Commanding Officer of No 4 Commando, Lord Lovat was awarded the Military Cross for his actions during a raid at Hardelot in April 1942.  He was further awarded the Distinguished Service Order for gallant and distinguished service during the Dieppe raid on 19 August 1942. In 1943, when the Commandos were organised into Special Service Brigades, he left No 4 Commando to take up a new command. 6 June 1944 D Day Officer Commanding 1st Special Service Brigade at Normandy, France.