In April 1937, the squadron was re-formed as No. 37 (Bomber) Squadron at RAF Feltwell in Norfolk, East Anglia from a nucleus provided by No. 214 Squadron RAF, equipped with the Handley Page Harrow heavy bomber. It re-equipped with Vickers Wellingtons in May 1939, retaining them at the outbreak of World War II, when it formed part of 3 Group. The squadron flew its first operational mission of the war on 3 September 1939, an unsuccessful armed reconnaissance mission by six Wellingtons to the Schillig Roads to search for German warships. On 18 December 1939, 37 Squadron contributed six aircraft to a sortie by 24 Wellingtons against shipping in the Heligoland Bight. The formation came under heavy attack by German fighters, with five out of 37 Squadron's six Wellingtons shot down, with 21 men killed. In total, twelve Wellingtons were shot down.