Her fifth patrol, in June 1940 was one of her most successful, making full use of the situation in Europe following the Fall of France. "U-48" was commanded by Hans Rudolf Rösing, as Herbert Schultze was hospitalised with a kidney and stomach complaint. She attacked three ships off the Donegal coast; "Stancor" carrying fish from Iceland, "Eros" carrying 200 tons of small arms from America and "Frances Massey" with iron ore. 34 sailors lost their lives on "Frances Massey". The cargo on "Eros" was particularly important following the losses at Dunkirk. The badly damaged "Eros" was taken in tow by , assisted by and and headed to the Irish coast, where "Muirchú" and "Fort Rannoch" were waiting for them. "Eros" was beached on Errarooey strand. While she was being repaired, Irish troops guarded the site.