'Regenbogen' (i) was the German naval undertaking against the JW.51B convoy, leading to the Battle of the Barents Sea (31 December 1942).

The battle involved the British warships escorting the convoy to the Kola Inlet in the northern USSR and a German surface raiding force.

The JW.51B convoy comprised the 6,131-ton Panamanian Ballot, 6,891-ton Panamanian Calobre, 5,078-ton US Chester Valley, 5,571-ton British Daldorch, 5,815-ton British Dover Hill which later turned back with weather and boiler damage, 7,031-ton British Empire Archer, 8,032-ton British Empire Emerald, 4,978-ton US Executive, 7,582-ton US Jefferson Myers, 7,191-ton US John B. Latrobe, 8,319-ton British Pontfield, 6,076-ton US Puerto Rican, 7,176-ton US Ralph Waldo Emerson, 5,670-ton US Vermont and 5,612-ton US Yorkmar. These ships were carrying some 202 tanks, 2,046 other vehicles, 87 fighters, 33 bombers, 11,500 tons of motor fuel, 12,650 tons of aviation fuel and slightly more than 49,000 tons of other supplies.

The 14 remaining merchant ships were escorted by the British destroyers Achates, Obdurate, Obedient, Onslow, Oribi and Orwell, the corvettes Hyderabad and Rhododendron, minesweeper Bramble, and the armed trawlers Northern Gem and Vizalma, under the command of Captain R. St V. Sherbrooke in Onslow.

In addition to the convoy escort, Rear Admiral R. L. Burnett’s Force 'R' (light cruisers Sheffield and Jamaica, and two destroyers) was operating independently in the Barents Sea to provide more distant cover for the convoy.

The German force, based in the Altafjord of northern Norway and commanded by Vizeadmiral Oskar Kummetz, comprised the heavy cruiser Admiral Hipper, the heavy cruiser (ex-pocket battleship) Lützow, and the destroyers Friedrich Eckholdt, Richard Beitzen, Theodor Riedel, Z 29, Z 30 and Z 31.

The JW.51B convoy departed Scapa Flow in the Orkney islands group on 22 December and met its escort off Iceland on 25 December. From there the ships sailed to the north-east, on 28/29 December encountering strong gales which scattered the ships. When the weather moderated, five merchantmen, Oribi and Vizalma were missing, and Bramble was detached to search for them. Three of the straggling merchantmen rejoined on the following day, and the other ships proceeded independently toward the Kola inlet.

On 30 December, meanwhile, the convoy had been sighted by U-354. When the report was received by the German naval staff, Kummetz was ordered to intercept and destroy the convoy. Kummetz divided his force into two divisions led by Admiral Hipper and Lützow.

Because the battle took place during the darkest time of the year, and because both the German and British forces were scattered and unsure of the positions of the rest of their own forces, let alone those of the enemy, the entire battle was confused. During the battle it was not clear who was firing on whom or even how many ships were engaged.

At 08.20 on 31 December Obdurate, stationed to the south of the convoy, spotted three of the German destroyers to the rear of the convoy in the west. Then Onslow spotted Admiral Hipper, also to the rear of the convoy, and moved to intercept with Obdurate, Obedient and Orwell, while Achates was ordered to stay with the convoy and make smoke. After some confused firing, Admiral Hipper effected a temporary retirement as Kummetz was worried that the destroyers were making a torpedo attack, and had been ordered not to risk his ships.

Admiral Hipper then made a second attack, hitting Onslow. Sherbrooke was badly injured by a splinter and passed command to Lieutenant Commander D. C. Kinloch, captain of Obedient. Admiral Hipper pulled away to the north of the convoy, encountered Bramble, and opened fire. Friedrich Eckholdt was ordered to finish the damaged Bramble, while Admiral Hipper shifted target to Obedient and Achates to the south. Achates was badly damaged and later sank.

The firing had meanwhile attracted the attention of Force 'R', which was still farther to the north. Sheffield and Jamaica opened fire on Admiral Hipper at 11.30. Kummetz initially thought the attack of the two cruisers was coming from another destroyer but, on realising his mistake, ordered his ships to pull away to the west. Friedrich Eckholdt mistook Sheffield for Admiral Hipper, and was quickly sunk. Meanwhile Lützow approached from the east and fired ineffectively at the convoy, which was still hidden by smoke from the sinking Achates.

Heading to the north-west to join Admiral Hipper, Lützow also found Sheffield and Jamaica, which opened fire. Coincidentally, just before 12.00 each side decided to break off the action at much the same time, fearing imminent torpedo attack on its major ships from the other side’s remaining destroyers.

Burnett’s Force 'R' continued to shadow the German ships at a distance until it was evident that they were retiring to the Altafjord, while the ships of the convoy re-formed and continued toward the Kola inlet.

The German attack on the JW.51B convoy was thus a complete failure since all the merchant ships ships reached their Soviet destinations. Even more critically for the outcome of the war, Adolf Hitler was so angry at what he perceived as the uselessness of the surface raiders that he ordered the entire German surface fleet to be decommissioned and scrapped, and for the German navy to concentrate exclusively on U-boat warfare. Grossadmiral Erich Raeder, supreme commander of the Kriegsmarine, offered his resignation and was replaced by Admiral Karl Dönitz.