Slow Convoy SC-48, consisting of 50 merchant ships in nine columns, sailed through the Straight of Belle Isle into the Atlantic on 10 October 1941. The weather deteriorated and eleven ships straggled, including that of the convoy commodore. On October 15 the reduced convoy, advancing at a speed of seven knots and escorted only by four corvettes, ran into a concentration of submarines about 400 miles south of Iceland. Three ships were torpedoed and sunk that night. Shortly after the attack began, the destroyer H.M.C.S. Columbia arrived. In response to an appeal for help, a division of five United States destroyers commanded by Captain L.H. Thebaud (PLUNKETT, LIVERMORE, KEARNY, GREER, DECATUR) and also H.M.S. BROADWATER and the French corvette LOBELIA, were collected from both Reykjavik, Iceland and a west-bound convoy. By sunset 16 October they had taken station. During the night, the wolfpack made six successful attacks. Since the escorts were stationed only 1000 to 1500 yards from the convoy, the U_boats were able to select long-range firing positions, 4000 to 5000 yards from the merchants, yet beyond the range of the destroyers' sound gear. United States destroyers were not yet equipped with radar, which might have enabled them to detect a surfaced enemy. When the first merchant ship was torpedoed, the escorts sent up star shell and dropped depth charges indiscriminately, which added to the general confusion. In a second attack, two more ships were torpedoed and sunk. Then came three attacks in quick succession that accounted for four more. A torpedoed ship about 1200 yards from the U.S.S. KEARNY was burning, which silhouetted the destroyer between her and the enemy. A torpedo then struck the KEARNY on the starboard side. On the 18th, the H.M.S. BROADWATER was torpedoed and had to be abandoned and sunk; GLADIOLUS, detached to screen a straggler, never returned.

Fundamental lessons in escort duty were expensively learned from the battle of SC-48. Destroyers had previously been ordered not to patrol at night or in thick weather; but it was now learned that rigid station-keeping merely invited attack. Aggressive night patrolling at distances of 2000 to 5000 yards from the convoy was now enjoined, more than double that of the earlier doctrine, in order to keep U-boats at a distance. Indiscriminate depth-charging was countermanded, as more embarrassing to floating survivors than to the enemy.