On 1 April 1918, Johns was appointed flying instructor at Marske Aerodrome in Yorkshire. The aircraft of the time were very unreliable and he wrote off three planes in three days through engine failure – crashing into the sea, then the sand, and then through a fellow officer's back door. Later, he was caught in fog over the Tees, missed Hartlepool and narrowly escaped flying into a cliff. Shooting one's own propeller off with a forward-mounted machine-gun with malfunctioning synchronisation was a fairly common accident, and it happened to Johns twice. The Commanding Officer at Marske was a Major Champion, known as 'Gimlet', a name used later by Johns for the hero of a series of stories.