Cranwell was selected as a centralised training centre for seaplanes, balloons and airships by the RNAS. It was selected for three reasons, room for expansion, close to proposed east coast postings and no outstanding natural features that would guide enemy aircraft to it. The RNAS base was named HMS Daedalus, and was opened on 1st April 1916. A dedicated railway line was built to Cranwell from the nearby Sleaford line. On 1st April 1918 the RNAS and RFC were merged to form the new service, the Royal Air Force, RAF. This move lead to Cranwell becoming the centre of officer training for the RAF ( see later ).

The Army and Navy were keen to regain control of their respective air arms after the war, but the new RAF had a commander, Trenchard, who foresaw a role for a separate force with its own college to rival Sandhurst and Dartmouth. He had his way and centred the college on Cranwell. The first courses were started in 1920, and each course lasted for 2 years. On Empire Day 1937, 9,000 people turned up to an open day werre displays were flown, although training remain the bases main task.