Nothing strange about them. Hunter-killer groups were one of the cornerstones of the successful allied ASW strategy. Captain
Johnnie Walker was in large part responsible for promoting this idea, and every time I run into a group of Black Swans, I sure do feel a bit of a chill... definitely one of the most determined threats you can meet!
"Walker led from Starling, a newly-commissioned Black Swan-class sloop. The group was intended to act as re-inforcement to convoys under attack, with the capacity to actively hunt and destroy U-boats, rather than be restricted to escorting convoys. Walker had suggested the innovative idea to Commander-in-Chief Western Approaches Command Sir Max Horton. The combination of an active hunting group and a charismatic, determined and innovative anti-submarine specialist such as Walker would prove to be a potent force.
Walker sank more U-boats during the Battle of the Atlantic than any other British or Allied commander and was instrumental in the Allied victory of the Battle of the Atlantic, one of the most important campaigns of the war. "
So in reality, you think you were stalking a task force, but it's actually a task force whose sole purpose is stalking you!