 On the first serious test of the system in 1942, a Wellington piloted by Greswell, located two U-boats and seriously damaged both with depth charges and machinegun fire.On his return from a detachment in the United States, where he had overseen American manufacturers on the fitting of the Leigh Light system in Liberators and trained aircrew in its use, Greswell was promoted to wing commander and posted to No.179 Squadron RAF in Gibraltar.