West joined the British Army in 1914 at the outbreak of war, later transferring to the Royal Flying Corps, training as an observer at Brooklands, and returning to France in April 1917. After six months and 225 flying hours he was posted back to Britain to undergo pilot training at Grantham. He was then posted to No 8 Squadron in January 1918. On 21 April 1918 West , witnessed the last combat and fall of Manfred von Richthofen.While flying a reconnaissance mission in August 1918 West and his observer spotted an enemy concentration through a hole in the mist. Avoiding severe ground fire, almost immediately they came under attack from seven German fighter aircraft and West was hit in the leg, and his radio transmitter was smashed.
Only when he was sure of the enemy's position did he attempt to break off and head for his own lines. He twisted his trouser leg into a tourniquet to stem the flow of blood from his wounds. Unable to make his airfield West landed behind the Allied lines and insisted on reporting his findings despite being in excruciating agony. His left leg had five wounds, one of which had shattered his femur and cut the femoral artery, and had to be amputated. Shortly afterwards he was invalided back to Britain, where on 9 November 1918 he learned that he had been awarded the Victoria Cross.

A Canadian national, Botterell joined the Royal Naval Air Service in 1916 and was sent to England for training, receiving his wings on August 15, 1917. In September, Botterell joined No. 8 Naval Squadron. The squadron, which was usually referred to as Naval 8, was soon posted to France in support of the Royal Flying Corps. Botterell's immediate superior was also a Canadian, the flying ace Flight Commander James White. The squadron was commanded by another ace, Squadron Commander Christopher Draper, who was later known as the "Mad Major" for his habit of flying under bridges.
On September 18, 1917, Botterell's second operational flight as a pilot ended in a crash at Dunkirk when the engine of his Sopwith Pup failed. He sustained head injuries, a fractured leg and broken teeth. After six months in hospital, he was discharged and sent back to Canada.
En route, Botterell ran into some of his former colleagues from Naval 8 in London. They arranged for him to be sent to Manston in Kent to try to re-qualify as a pilot. After 10 hours of refresher training, he was approved to start flying once more and was sent to Serny on the Western Front, where he rejoined No. 8 Naval Squadron, now renamed No. 208 Squadron RAF. He served with them from May 11 to November 27, 1918, flying a variety of missions in different aircraft. He flew patrols and fought over Serny, Tramecourt, Arras, Foucaucourt and Estrées. In 60 days between June and August 1918, he flew 91 sorties.

When the First World War broke out in August 1914, Harris did not learn of it for nearly a month, being out in the bush at the time. Despite his previous reluctance to follow the path his father had had in mind for him in the army, and his desire to set up his own ranch in Rhodesia, Harris felt patriotically compelled to join the war effort. He quickly attempted to join the 1st Rhodesia Regiment and was sworn in on 20 October 1914.
The 1st Rhodesia Regiment served alongside the South African forces in South-West Africa during the first half of 1915. When the campaign ended in July 1915, the 1st Rhodesia Regiment was withdrawn to Cape Town, where it was disbanded; Harris was formally discharged on 31 July. In August he sailed for England arriving in October, after unsuccessfully attempting to find a position in first the cavalry, then the Royal Artillery, joined the Royal Flying Corps as a second lieutenant on probation on 6 November 1915.

Harris learned to fly at Brooklands in late 1915 and, having been confirmed in his rank, then went on to serve with distinction on the home front and in France during 1917 as a flight commander and ultimately CO of No. 45 Squadron, flying the Sopwith 1½ Strutter and Sopwith Camel. Before he returned to Britain to command No. 44 Squadron on Home Defence duties, Harris claimed five enemy aircraft destroyed and was awarded the Air Force Cross (AFC) on 2 November 1918. He finished the war a major.

Harris was one of the most prominent figures of WWII as head of RAF Bomber Command, and the architect of history’s most intense bombing campaign.

SSoon after outbreak of the First World War, Park enlisted in the New Zealand Expeditionary Force (NZEF) on 14 December 1914, and was posted to the Field Artillery. In March, Park's battery, along with the rest of the 29th Division, was shipped to the Western Front and assigned to a sector along the Somme. On 21 October, while trying to withdraw an unserviceable gun for repair, Park was blown off his horse by a German shell. Wounded, he was evacuated to England and medically certified "unfit for active service", which technically meant he was unfit to ride a horse. After a brief remission recovering from his wounds, he joined the Royal Flying Corps (RFC) in December.
In June he was posted to France, where he joined No. 48 Squadron, a fighter unit at La Bellevue. Shortly after Park's arrival at No. 48 Squadron, the unit moved to Frontier Aerodrome just east of Dunkirk. The squadron was equipped with the new Bristol Fighter, a two-seat biplane fighter and reconnaissance aircraft, and carried out patrols and reconnaissance flights. By the end of the war Park had been credited with 14 aerial victories.

Following the outbreak of the Second World War Park joined Fighter Command and became commander of No. 11 Group, the group responsible for the fighter defence of London and southeast England, the area of the most intense air fighting during the Battle of Britain.