Under the command of Captain Heinrich Timm, U-251 left Germany in April 1942 and sailed up to northern Norway where they used the port of Kirkenes as a base for their operations.

U-251 was one of the so-called grey wolves. These hunted and attacked in packs and were very effective war machines. However, they had a great limitation in the speed and time they could be submerged. Therefore, they ran their diesel engines in surface mode as often as possible and mostly only dived when they attacked. When a convoy was spotted, the tactic was to pursue it until more submarines had joined and it became dark.

On patrol between 29 April and 7 May 1942, a convoy, PQ15, was discovered, which was on its way with war munitions to Russia. It was pursued and more units were called in. KI 2327 on 3 May the Luftwaffe attacked the convoy in formation with 6 aircraft and shot down torpedoes. The British opened fire and two of the aircraft were hit by British fire and crashed into the sea. Two ships, S/S Botavon and Cape Corso, were sunk by the bombers. At 0014, U-251 attacked. Three torpedoes were fired from tubes 1, 2 and 4. Tube 3 was not ready to fire at the time. At 0022, the torpedoes were heard exploding and the British cargo ship S/S Jutland sank. The crew of the sunken ship were picked up by British ships.

On board the British ship HMS Leda, at 0139, U-251 had been sighted when it dived and they set course straight for it. At 0142, the ship dropped 4 depth charges, set to detonate at a depth of between 40 and 80 m, against the German submarine. After dropping the depth charges, HMS Leda lost contact with the submarine and at 0215 the search was called off and returned to the convoy, believing that the submarine had either been sunk or damaged. On board U-251 the crew had heard the depth charges fall and explode but at a distance enough to be safe and at 0342 the threat was considered over and they surfaced.

On 6 July 1942 U-251 set out from Harstad in northern Norway, to patrol until 15 July. U-251 was on a search for targets together with U-376, U-88, U-355, U-457 and U-657. Together they formed the wolf pack “Eisteufel”, the “Ice Devils”.

On 10 July, convoy PQ17 was attacked, one of the most notorious convoys of World War II, with about 40 ships involved and almost all of them sunk. At 0046, U-251 fired a well-aimed torpedo from tube 3 at the cargo ship El Capitán. The ship, which was heading for Russia with war weapons, had been attacked earlier in the day by the Luftwaffe and 64 men were on board when it was torpedoed. One man died. The others were rescued aboard a British ship. After attacking the convoy, a British destroyer pursued it and at 0052, a torpedo was fired from the stern, tube 5, but it missed its target. At 0313, depth charges were heard falling but at a safe distance. After completing the patrol, it arrived in Narvik on 15 July.

On 16 April 1945, it left Kiel under the command of Franz Säck. Heinrich Timm now commanded U-862 where he managed to sink 7 ships before the submarine was seized by the Japanese in Singapore on 6 May 1945 and renamed 1-502. Heinrich Timm was released from his captivity on 9 April 1948.

On 19 April 1945, U-251 was in the Kattegat, along with U-2502 and U-2335, and M-403, en route from Kiel to Norway. At 1623, 22 British Mosquito planes were seen approaching, along with some Mustang planes, and an air raid alert was given. At 1630, the convoy was attacked. After a short battle, U-2502 and U-2335 managed to dive and escaped the attack with only minor damage, and later arrived in Norway after a short stop in Aarhus for repairs. U-251 and M-403 were not so lucky. U-251 fired at the aircraft with her 2 cm and 3.7 cm guns but was hit both fore and aft and the ship began to take on water. The order to get out of the ship was given and a signal was given to U-2502 that she was sinking rapidly. It was now 1635 and a new wave of attacks began against U-251 by the British aircraft. A large part of the crew had now got out of the boat and the 3.7 cm gun was manned and the rest of the crew took cover behind the turret. The British bombers scored three hits and the submarine sank and the order to abandon ship was given.

M-403, which was only a short distance away, came to the rescue of the crew but the ship was also hit by the bombers and sunk. The crew from U-251 were now in the icy water. The water temperature was 5 degrees. After 20 minutes in the water, the first crew members perished due to the cold. Later, 6 men, severely chilled, were rescued on a life raft. A short while later, two of them died. After 2.5 hours in the water, U-2502 was seen to surface and its attention was called. The four survivors were taken aboard and a search was made for more survivors, but only scattered wreckage was found, seemingly floating in the water.

During the battle with the Germans, three aircraft were hit by German anti-aircraft fire. A Mosquito plane managed to make an emergency landing in Denmark. A Mustang plane, KH695, which had been escorting the Mosquito plane, made an emergency landing on Getterön outside Varberg. The pilot was unharmed. 15 minutes later, Mosquito RS612 flew into Halmstad. The plane sent out distress signals while making a few turns over the city. When passing Tylösand, the landing gear was deployed and shortly afterwards the crew of the F14 made an emergency landing in Halmstad. The plane was riddled with bullet holes and the right propeller was shot out. The two crew members were unharmed and were happy to have ended up in neutral Sweden. They reported that the aircraft had been damaged when attacking German submarines in the Kattegat. At the time of the incident, the Hallandsposten newspaper reported that both crew members were in their 25s and that they were treated to the Swedish military’s main dish: peas with pork. It was also explained that the two Britons thought the delicacy tasted excellent.

Today, the wreck of U-251 stands keel-down on a hard sandy bottom off Anholt. The ship is relatively intact, although traces of the battle when it sank can be seen. Since the bottom is quite hard at the site, the wreck has not sunk too far into the bottom, which means that the propellers and rudders in the stern are very clearly visible. There are a number of holes to look into at various places on the wreck. In the tower, for example, you can see straight down and into the submarine.