As U-48 cruised to the West of the Western Approaches, two days after Britain and Germany went to war, she spotted her first target, the 5,000 ton SS Royal Sceptre, sinking her and two more unescorted ships as she returned to Kiel via the North Sea on 17 September. Her second patrol was even more successful, catching several allied ships unawares in the same area as her previous victories, including the large French tanker SS Emile Miguet on 12 October. Four more freighters were sunk on this cruise, during which the U-48 was largely untroubled by Allied countermeasures.
She sank another three on her final patrol of 1939 and damaged another, including two neutral ships operating in allied controlled areas. After a brief break over the Christmas period, she again put to sea, sinking the British Blue Star Line liner SS Sultan Star in the Western Approaches, it was only carrying freight. A string of mines she laid off St Abb's Head failed to have effect, but two neutral Dutch ships were added to her tally shortly afterwards, as well as a Finnish ship, all of them operating in the North Atlantic in cooperation with the Allied convoy system.
Her fifth patrol, in June 1940 was one of her most successful, making full use of the confusion in Europe following the Fall of France to leave a trail of destruction on her passage around the British Isles sinking three ships on her passage to the Atlantic Ocean, and enjoying an extended patrol thanks to the newly established refuelling facilities available at Trondheim in Norway. In all she claimed eight ships from the convoys in the Eastern Atlantic on this cruise, and bagged five more on her sixth patrol in August, which finished with her stationed at Lorient in France, greatly extending her raiding abilities.
In September, on her seventh patrol she shocked the world by sinking the SS City of Benares, one of eight ships in six days from Convoy SC-3 and Convoy OB-213. Benares was a refugee ship, carrying children from Britain to Canada to keep them safe from The Blitz on Britain's cities. 258 people, including 77 children, were killed. Amongst the other sinkings was the British frigate HMS Dundee. Her eighth patrol was also highly successful, sinking seven ships out of Atlantic convoys, including one from Convoy SC-7. The operating zone for both these patrols was far to the North of her previous areas, being south of Greenland.
Although on her ninth and tenth patrols the U-48 claimed two and five victims respectively, she was clearly beginning to become obsolete in the face of improving technology on both sides despite a winter refit. Her range and torpedo capacity were too small for the widening nature of the sea war, and she would be a risk to her crew and other U-boats if she continued much longer in the main battlefield of the North Atlantic. On her final patrol she sank five more ships, the boat boosted by the award of the Knight's Cross to Erich Zürn, the boat's executive officer, for his success and judgement during the ships's career.
U-48 returned to Kiel on 22 June 1941, where her crew were removed, and she was transferred to a training flotilla operating exclusively in the Baltic Sea. Unlike many of her contemporaries, U-48 never sailed on patrols against Soviet targets following Operation Barbarossa the following month, and in 1943 was deemed unfit even for this reduced service, being laid up at Neustadt in Holstein with only a skeleton crew performing minor maintenance. It was there she remained for the next two years, until the maintenance crew, realising that the war was ending and the boat would be captured, scuttled her in the Bay of Lübeck on 3 May 1945, where she remains.
The sinking of the City of Benares
In the late hours of the 17 September 1940, U-48 put a single torpedo into the 11,000 ton liner SS City of Benares, flagship of Convoy OB-213, as she was silhouetted against the moonlight in the mid-Atlantic. Unbeknownst to Kapitänleutnant Heinrich Bleichrodt, on board the liner were 90 children being evacuated to Canada under the Children's Overseas Reception Board's initiative in order to escape the effects of the Blitz.
The sinking ship took on an immediate list, thus preventing the launching of many of the liferafts and trapping numerous crew and passengers below decks. As a result, many of the 400 people on board were unable to escape. As hundreds of survivors struggled in the water, the U-boat's powerful searchlight swept once over the chaotic scene, before the boat left the area for good. The survivors in the boats were not rescued for nearly 24 hours, as the nearest Allied units were 300 miles away, and in that time dozens of children and adults died from exposure, or drowned, leaving only 148 survivors. One boat was not picked up for a further eight days. In total 258 people, including 77 of the evacuees, died in the disaster, which effectively ended the overseas evacuation program.
The controversy of the City of Benares disaster has been debated ever since.. It has been suggested that had the British openly declared that the ship was carrying evacuees, then the Germans would have taken pains not to sink it, recognising the potential for a propaganda crisis, which indeed occurred. However, the ship was not only travelling unlit at night in an allied convoy, but it was also the flagship of Rear-Admiral Edmund Mackinnon, the convoy commander. Other historians have argued that the Germans would have attacked any large liners at the time, no matter the cargo or the passenger list. Finally, it is unlikely that Bleichrodt was able to see that there were children amongst the wreckage from his single sweep, and was also keenly aware of his vulnerable position close to his two latest victims, which compromised his ability to provide aid even he had wished to do so.