 It was to act as reinforcement to convoys under attack, with the capacity to actively hunt and destroy U-boats, rather than be restricted to escort duties.Comprising six sloops of the "Black Swan"-class, the group was led by Captain F.J. "Johnnie" Walker, Britain's most successful anti-submarine warfare commander, in .The combination of an active hunting group and a charismatic, determined and innovative anti-submarine specialist such as Walker proved to be a potent force; 2 SG was the most successful anti-submarine unit of the war, being credited with the destruction of 23 U-boats during two years of active service.