'Juno' (i) was a German naval raid off the west coast of Norway by the battle-cruisers Scharnhorst and Gneisenau, accompanied by the heavy cruiser Admiral Hipper, together with the destroyers Karl Galster, Hans Lody, Erich Steinbrinck and Hermann Schoemann, under the command of Vizeadmiral Wilhelm Marschall, and was designed to interrupt the flow of Allied troops and equipment from France and the UK to Norway in the campaign which followed 'Weserübung' (4/9 June 1940).

Originally scheduled for 25 May, the sortie was intended to reduce the pressure on the German land forces at Narvik by means of attacks on Allied ships and shore installations. It was a bold plan and, in view of a great reduction of the British naval strength available to Admiral of the Fleet the Lord Cork and Orrery, commanding in the area, could have succeeded in causing the Royal Navy heavy losses.

The German move was delayed, however, and the ships finally departed Kiel on 4 June with the intention of striking at Harstad on the night of 8/9 June after refuelling off Jan Mayen island. The German squadron was screened during its passage through the Kattegat by the torpedo boats Falke and Jaguar, mine barrage breaker Sperrbrecher 4 (6,757-ton ex-mercantile Oakland), tender Hai and a number of motor minesweepers. The torpedo boats remained with the force through the Skagerrak.

The Germans were unaware at the time of the fact that the Allies had abandoned the Norwegian campaign and were therefore evacuating their forces, and that large convoy movements were currently taking place across the northern section of the North Sea. On 7 June, however, German air reconnaissance reports of two groups of Allied ships were transmitted to Marschall, who decided to attack the more southerly group. This led to the sinking, on the morning of 8 June, of the tanker Oil Pioneer, her escorting anti-submarine trawler Juniper and the 19,777-ton commissioned troopship Orama, which was returning to England empty and independently, but not the hospital ship Atlantis, which was with Orama.

Under the control of Generaladmiral Alfred Saalwächter’s Marinegruppenkommando 'West', the Oberkommando der Kriegsmarine element responsible for naval operations in the west, Marschall was to delegate further attacks on the convoys to Admiral Hipper and the destroyers, and to switch his main strength to his specified task, namely an attack on the British naval forces and shipping around Harstad. By this time Marschall had deduced that an evacuation was in progress, and did not carry out these orders. Admiral Hipper and the destroyers were detached to Trondheim on 8 June as they could not be refuelled at sea, while the battle-cruisers continued to search for targets.

On 10 June the refuelled Admiral Hipper attempted to leave Trondheim, but was forestalled by the sighting of a British submarine.

In the afternoon two German warships chanced on the elderly fleet carrier Glorious, escorted only by the destroyers Acasta and Ardent. Early in the morning of 8 June the carrier had completed the difficult task of flying on RAF land-based fighters (eight Hawker Hurricane monoplane and 10 Gloster Gladiator biplane machines of Nos 263 and 46 Squadrons) for evacuation: the difficulty of the task was increased by the fact that none of the aircraft had an arrester hook and were being flown by pilots without any experience of making a deck landing. The carrier then departed for home as part of a troop-evacuation convoy, which also included the more modern fleet carrier Ark Royal, but then requested and received permission to proceed independently because she was short of fuel or, according to other sources, because her captain, Captain G. D’Oyly-Hughes, was impatient to return to Scapa Flow as quickly as possible to appear as a witness in the court martial of the ship’s air commander, whom D’Oyly-Hughes had left at Scapa Flow after he had refused to plan and execute attacks on land targets on the grounds that Glorious's aircraft were unsuited to the task.

The carrier had five Fairey Swordfish biplanes with which to maintain reconnaissance flights and even to constitute a small attack force, and also nine Sea Gladiator fighters with which to fly combat air patrols, so it is strange that the carrier neither flew off patrols for her own protection, nor kept at readiness an attack force. Moreover, only 12 of the carrier’s 18 boilers were being used, which limited the Glorious's speed to 17 kt, and the visual watch for German ships had been entrusted to the destroyers, whose low lines provided considerably shorter horizons than the carrier’s tall island and mast. Thus the carrier was caught not only unawares but virtually without means of defence when the German battle-cruisers sighted her smoke at 16.00 in the Norwegian Sea.

Scharnhorst opened fire some 30 minutes later with her 11-in (280-mm) main guns at a range of 27,885 yards (25500 m), well beyond anything to which the carrier’s 4.7-in (119-mm) armament could respond. The German gunnery was very accurate, and heavy shells soon caused damage in the carrier’s hangar spaces, so preventing the arming and launching of the Swordfish aircraft in their torpedo bomber role. Gneisenau also opened fire, her salvoes hitting the carrier’s island and bridge.

The destroyers headed at maximum speed toward their much larger foes and laid a smoke screen which, for a time, shielded Glorious from the German ships' heavy shells. But this brave action could only postpone and not halt the destruction of the carrier, for at about 17.20 Glorious had stopped, blazing furiously, and her crew were abandoning ship. Only eight minutes later Ardent, having fired all her torpedoes, was overwhelmed and sank. At about 17.40 the carrier capsized and sank. Alone and facing genuinely insuperable odds, Acasta turned again toward the German capital ships with her 4.7-in (119-mm) guns blazing and fired a salvo of four torpedoes, one of which hit Scharnhorst abreast her after turret and caused major damage as well as killing 50 men and causing the ship to take in 2,500 tons of water. At 18.08 Acasta too went down.

In order to conserve ammunition, Marschall had ordered his ships to cease fire before Glorious sank, and the two German ships then headed for Trondheim for emergency repairs to Scharnhorst, not pausing to rescue survivors as the ships were now in an exposed position without naval or air cover and possibly facing substantially larger British forces facing to the scene. On 13 June, Blackburn Skua dive-bombers of the Fleet Air Arm operating from Ark Royal attacked Scharnhorst and secured one bomb hit, and it was not until 23 June that the battle-cruiser was able to reach Kiel and a dry dock. She remained there under repair for most of the rest of 1940.

The loss of one of the Royal Navy’s few carriers was serious, and so too were the destruction of so many aircraft and many invaluable naval and 63 aircrew among the 1,533 men lost. On 11 June three officers and 35 men from Glorious and one from Acasta were picked up by Borgund, a small Norwegian merchant vessel and landed at Tórshavn in the Færoe islands group on 14 June. Another Norwegian vessel rescued five men from Glorious who, with two from Ardent picked up by a German seaplane, were made prisoner. All the rest of the three crews went down with their ships.

The last fight of Acasta and Ardent, and the damaged inflicted on Scharnhorst by Acasta, probably saved Cork’s lightly escorted convoy, which was coming down from the north through the same area: the German battle-cruisers abandoned the operation and made for Trondheim, which they reached in the afternoon of 9 June.

The news of this desperate battle was slow to reach Admiral Sir Charles Forbes, commanding the Home Fleet, because the carrier’s radio equipment had been wrecked early in the action, and it was the hospital ship Atlantis which gave the first news of the German presence when she met the battleship Valiant on the morning of 9 June, some 24 hours after the sinking of Orama. The battleship was hastening back from escorting the first group of troopships to join the second, now some 400 miles (645 km) to the north of her, and at once forwarded the information. This transmission produced a signal from Vice Admiral J. H. D. Cunningham in the heavy cruiser Devonshire who, with the king of Norway on board, had left Tromsø on the evening of 7 June, for he had picked up a cryptic message from Glorious referring to an earlier message and reporting two pocket-battleships.

Cunningham had refused to break wireless silence to pass on this garbled message and thus reveal the position of his ship while on so important a mission. It was not until the Germans broadcast their success during the afternoon of 9 June that Forbes finally began to gain an accurate impression of events. Forbes then sailed from Scapa Flow with the battleship Rodney, battle-cruiser Renown and six destroyers, and also ordered other redispositions to protect the returning convoys.

After the sinking of Glorious, and in company with Gneisenau, Scharnhorst made for Trondheim for repairs. As a result of their exposed position, the German ships could not tarry to stop and rescue survivors of any of the ships they had sunk. On 13 June, 15 Blackburn Skua bombers from the fleet carrier Ark Royal attacked Scharnhorst in harbour, and hit her with just one bomb. Eight of the Skua aircraft were lost in the process, and realisation of the Skua’s inadequacies resulted in the type’s withdrawn from front-line services in 1941.

As a result of the action, 1,519 British servicemen on board Glorious, Acasta and Ardent lost their lives, sa figure which exceeded that of any of the other great British naval disasters of the war. Along the three warships, two RAF fighter squadrons were lost.

The emergency repairs to 'Scharnhorst's torpedo damage lasted to 23 June, and the ship then steamed to the south to reach Kiel and a dry dock. She remained there under repair for most of the rest of 1940. Although Glorious was a major loss, the withdrawal of the two powerful German battle-cruisers allowed the remaining Allied evacuation convoys to reach the UK with a greatly reduced threat.