Orlebar was commissioned as a
second lieutenant in 1/5th Battalion,
Bedfordshire Regiment (
Territorial Force) on 15 January 1915. His battalion landed at
Suvla Bay on 11 August 1915, pitching him into the
Gallipoli campaign, He was promoted to temporary
lieutenant on 21 September 1915, but was subsequently wounded in action by a sniper's bullet. He was then invalided to the United Kingdom and seconded to the
Royal Flying Corps (RFC) on recovery. Orlebar trained as a pilot in 1916 and was appointed a flying officer in the military wing of the RFC on 17 September 1916 when he was formally seconded from his regimental duties to the RFC. His rank of lieutenant was confirmed on 21 October. He was posted to
No. 19 Squadron RFC on the
Western Front. On 13 March 1918, he shot down and severely wounded
Ltn. Lothar von Richthofen (brother of
Manfred von Richthofen), near
Cambrai. He was wounded in turn himself by
Albatros scouts over Ham on 23 March 1918. Before his return to combat, he also served as an instructor in Essex. Orlebar was credited with two enemy aircraft destroyed whilst serving with No 19 and a further four as a flight commander in No 73 Squadron, before being wounded. He gained his final victory with No. 43 Squadron on 29 September, bringing his total to seven. ==Inter-war service==