7th June 1940
Operation Juno began before midnight, as the battlecruisers slipped their moorings and joined up with the Admiral Hipper and the destroyer escort (Karl Glaster, Hand Lody, Erich Steinbrinck and Hermann Schoemann), heading for Bodo. The original plan had suggested an attack on Harstad, much closer to Narvik, but with the continuing presence of naval units off Norway, this was felt as too dangerous. Instead the ships would bombard Bodo (still a base for Allied operations), and sink any shipping they encountered.
The main force in the Norwegian Sea belonged to the Royal Navy. While the ground force was an Allied operation, the situation in Europe had led to light units being retained there, and with the French heavy ships guarding the Mediterranean to keep the Italians honest, the fleet had been British. This was soon to change; with a reduced threat seen in the Mediterranean, and the need to show more Allied solidarity and joint operations after the battles in France and Belgium, the French navy had detached a group of two heavy cruisers and three destroyers. Given the length of the Norwegian shoreline to be covered, and the danger posed by air attack to operating as single ships, this would allow greater coverage. With an Allied infantry force soon to be landed at Mo-i-rana, this was seen as being very helpful.
While the Royal Navy actually had a sufficiency of heavy ships, it had been difficult to deploy them due to a lack of destroyers. After the earlier battles off Norway, the U-boat threat was seen as the main risk, along with air attack. The land fighting in Belgium had led to some destroyers being held ready for action off the coast if it had proven necessary, but now that things seems to be more stable, some had been released to Rosyth to refuel and be ready to escort HMS Warspite when she arrived.
The main role of the fleet was twofold; to support the troops ashore in Norway and especially the port of Narvik, and to cover any attempts by the remaining German heavy ships to break through so as to be able to attack the Atlantic convoys. The second role had resulted in the despatch of a heavy force centred around the battlecruisers Renown and Repulse to investigate a report that suggested a possible breakout. The main force was at sea to the west of Narvik, and the Aircraft Carrier Ark Royal, with two cruisers and ten destroyers. This would be reinforced on the 8th by the carrier Glorious - escorted by two destroyers, she was flying off 15 replacement Hurricanes today, and once they were gone her decks would be clear for normal flying operations.
The landing force for the M-i-rana attack would sail on the 8th; by this time HMS Warspite and her escorts should have arrived from Rosyth, and they would be the heavy escort for the supply ships. The convoy itself would have a close escort of four destroyers and two minesweepers. The French force would position itself south of these groups, to serve as warning and protection from any southern attack. A surprise attack by some of the Kreigsmarine destroyers was a possibility.
The Kriegsmarine did in fact have two destroyers in the area, but they weren't intending to attack the Royal Navy; they were the escort for a mixed group of small craft carrying around a battalion of troops to reinforce the defences to the east of Mo-i-rana. Admiral Marschall's heavy ships were to move past them, and tempt the heavier ships away from the area. Luftwaffe reports had shown that there were ships operating in small groups away from the protection of the heavy ships, and any of these they found would be sunk. Marschall intended to 'trail his coat' to the west, and then slip the Hipper and some destroyers in to attack Bodo.
The Kriegsmarine was also using the operation to cover the withdrawal of the cruiser Emden from Oslo. No longer seen as needed there, she sailed early on the 7th to meet up with the battlecruisers, and would then operate with Hipper to attack coastal targets and any coastal shipping they encountered.
While Marschall did not expect his sortie to actually stop the Royal Navy operating in the Norwegian Sea - the forces available to them, even without withdrawing any units from other theatres were simply too powerful - he could sink any ships he found away from the main fleet, and cause confusion. This would mean the Royal Navy would have to supply and keep operational more ships, and keep them in larger formations, limiting their tactical use and making them better targets for the U-boats.
8th June
The first contact was early in the morning, when the battlecruisers sighted a small group of ships. These were the oil tanker Oil Pioneer and her escort, the minesweeping trawler Juniper. These were heading back to Britain to take on more oil, and on seeing them Marschall ordered his cruisers to sink them, then head east towards Norway. His radio department had heard the ships reporting his position before the shells from Emden silenced them, and his intention was to split his force and see what he could find further north. Despite the instructions not to risk his ships unnecessarily, he intended to patrol aggressively, confident his battlecruisers could handle any single heavy ship. If he ran into a more powerful force, his speed would allow him to escape the older and slower Royal Navy battleships.
HMS Valiant and her escorting destroyers had arrived off the coast at 0700 that morning, staying well to sea of the troop convoy and serving as their heavy escort. HMS Warspite and the French cruiser force had left Rosyth the previous morning, having refuelled overnight, and would spilt up, the cruisers moving south of the convoy, while Warspite joined with the Ark Royal and Glorious. The news of attack on the tanker and her escort was a surprise, but not totally unexpected. The report had mentioned 'heavy ships', but with no confirmation it wasn't clear if this was correct or the notoriously poor ship recognition merchant ships often suffered from. The sudden ending of the transmissions indicated that whatever it was, it was a German warship. Needing more information, Glorious was ordered to send up six swordfish to sweep the area north and east of the report. The RAF was also notified, and asked to have fighters ready in case the ships were a diversion to pull the force into a Luftwaffe ambush.