The squadron's WW2 incarnation began when 137 was ordered to be formed at RAF Colerne in Wiltshire. The squadron was to be the second to be equipped with Whirlwinds and would be part of Fighter Command. However, the squadron was eventually formed at RAF Charmy Down under the command of S/L Sample on 20 September 1941. Six officers were posted from 263 squadron to form the core of the new squadron. Eighteen Whirlwinds had reached the squadron by 30 September 1941.
Their first operational flight was made on 24 October 1941.
In November 1941, 137 moved briefly to RAF Coltishall and relocated to Matlaske in Norfolk on 1 December 1941
In 1942, 137 entered into the fray against the Axis powers, achieving victories but suffering losses. It also took on the role of ground-attack squadron and began it's association with RAF Manston.
By June 1943, the squadron had been led to believe it would re-equip with Hawker Typhoons and some pilots had commenced training on this controversial new aircraft. However, a number of Hurricane IVs were delivered to the squadron instead of the expected Typhoons. The Hurricane IV featured a "universal wing" that allowed carriage of a variety of powerful ordnance. The squadron would re-equip with these Hurricanes, using both the potent 40mm cannnon and the then relatively untested rockets. It was the latter that would become the weapon synonymous with 137's operations from 1944 to 1945.
The last Whirlwind sortie was flown on 21 June 1943. Trains were shot up and bombed. The squadron would move to Rochford near Southend-on-Sea in order to "work up" their skills with the Hurricanes.
After 6 months of success with the Hurricane, in January 1944, 137 began to be re-equipped with Typhoons.