On November 19, 1942, Admiral Noble was replaced as Commander-in-Chief of Western Approaches Command by Admiral Sir Max Horton. Horton used the growing number of escorts becoming available to organise "support groups", to reinforce convoys that came under attack. Unlike the regular escort groups, support groups were not directly responsible for the safety of any particular convoy. This gave them much greater tactical flexibility, allowing them to detach ships to hunt submarines spotted by reconnaissance or picked up by HF/DF. Where regular escorts would have to break off and stay with their convoy, the support group ships could keep hunting a U-boat for many hours. One tactic introduced by Captain John Walker was the "hold-down", where a group of ships would patrol over a submerged U-boat until its air ran out and it was forced to the surface; this might take two or three days.