Operation HERMETIC: Countering the Threat to D-Day from the German Surface Fleet
It was a signal that Admiral Sir Bertram Ramsay must have been longing to send while being concerned at the potential consequences: ‘CARRY OUT OPERATION HERMETIC’. The issue of this simple order would have executed the contingency plan he had devised as Allied Naval Commander, Expeditionary Force to counter any attempt by the remaining major warships of the German Navy to attack the D-Day landings. It was one of the most interesting papers I discovered in the National Archives at Kew (in AIR 37/1453) while I was researching some primary material for the introduction of my volume on Operation NEPTUNE. Not least, it helps to counter the inaccurate but frequently held assumption that battleships were obsolete in the age of air power and were by this stage of the war entirely lacking a role in naval strategy.
Accounts of the D-Day landings all too often begin on the beaches and focus upon what happened subsequently, overlooking the vast challenges of the cross-Channel assault itself. Operation NEPTUNE, the amphibious landing that began Operation OVERLORD, was arguably the most complex military operation ever attempted. Among the enormous number and range of issues that the planners had to address, it is easy to overlook the imperative to neutralise Germany’s surviving surface warships. Countering the threat that these units posed remained largely a role for the Royal Navy: although Coastal Command became increasingly effective during the war, it was starved of resources by the leadership of the RAF while Bomber Command, despite the boasts of Arthur Harris during and (even more) after the war, had demonstrated little inclination or ability to target German warships.
The German fleet had been severely weakened by the late spring of 1944. Two of its three battleships had been sunk. Bismarck had been destroyed in May 1941 by a British naval force led by the battleships HMS King George V and Rodney, after being slowed by carrier-based aircraft from HMS Ark Royal. This victory was followed in December 1943 when a Royal Navy surface force led by the battleship HMS Duke of York had sunk Scharnhorst. The pocket battleship Admiral Graf Spee had in December 1939 been damaged by cruisers and was then scuttled rather than face what her captain believed to be a force of British capital ships. Some German warships had been temporarily put out of action by air mining or bombing, notably the battleship Gneisenau which was sufficiently badly damaged during a raid on Kiel in February 1942 to require a major rebuild. It is striking that by this stage in the war, the only German capital ships to have been sunk had fallen victim to other warships, not land-based air power. (A heavy cruiser, Blücher, had remarkably been sunk by Norwegian coastal artillery and torpedo batteries in April 1940.) It was also primarily the fear of British warships – in particular the combination of battleships with carrier support – that kept most of the remaining German major naval units confined to port. The general passivity of these warships infuriated Hitler, but they were a formidable potential force, a ‘fleet in being’ that caused much concern to Allied planners.
Despite the losses suffered, the German Navy could still have put a highly capable fleet to sea in late spring 1944. This could have included the battleship Tirpitz, the pocket battleships Lützow (the renamed Deutschland) and Admiral Scheer, and the heavy cruisers Prinz Eugen and Admiral Hipper, supported by four light cruisers and numerous destroyers. The threat these units posed could have been further increased through coordination with E-boats, U-boats and land-based aircraft.
British intelligence assessments saw any intervention by the major German warships as unlikely. Indeed, given the overwhelming naval preponderance of the Allies, it is entirely conceivable that an order for a major sortie would have elicited the same response from the German crews as from their predecessors in the High Sea Fleet, who had mutinied rather than participate in a ‘death cruise’ in October 1918. The far more likely naval threats, which accordingly dominated the attention of those planning Operation NEPTUNE, were mines, E-boats and U-boats. While these could have imposed grievous losses, it was only the enemy surface fleet that could conceivably have defeated the landings at sea. However low the probability of such an operation (their poor serviceability was not known at the time), it had to be considered, and a counter devised. The attention devoted to doing so suggests that the British had learned from the chastening experiences of the invasion of Norway and the ‘Channel Dash’ that the German Navy was quite capable of seizing the initiative and doing the unexpected in a highly competent fashion. The prospect of it doing so again, seeking to turn the tide of the war in the west even at this late stage, could not be ignored.
The first line of defence against any such sortie was the Home Fleet of the Royal Navy, based in Scapa Flow, with three battleships and three carriers. Two of the latter, HMS Furious and Victorious, reduced the potential threat in April 1944 with Operation TUNGSTEN, a highly successful attack that inflicted serious damage on the Tirpitz (which had only just finished repairing the damage inflicted by midget submarines in September 1943). She was thereby kept out of the Normandy campaign and was not included in the potential enemy force detailed in Ramsay’s memorandum. The Home Fleet after that provided cover against any German breakout (especially into the North Atlantic, seen as the most likely course of action). At the same time, it conducted strikes against targets ashore and obvious beach reconnaissance flights in Norway, in support of the Allied FORTITUDE NORTH strategic deception campaign. These operations were intended to help keep the German Navy in two minds as to where its efforts should be focussed. The cover role performed by the Home Fleet aimed to contain and, if necessary, attack any German naval breakout. Should such a sortie evade this force, an even more daunting obstacle would stand between it and the vulnerable supply shipping in the English Channel.
The plan for Operation HERMETIC, ‘to deal with a possible breakout through the Straits of Dover by some or all effective main units of the German fleet subsequent to D-Day’, was outlined by Ramsay in a memorandum of 24 May 1944. He expressed the hope that there would be an early warning of any such operation from intelligence, whether that was information that the warships concerned were redeploying to more westerly bases or increased minesweeping along their intended route. Unmentioned but no doubt in his mind was the likelihood of Ultra signals intelligence providing notice of enemy intentions. Should indications of a sortie become apparent, the Allies would increase air reconnaissance over the North Sea and would aim to bomb the enemy ships in harbour (although the meagre results achieved to date by such efforts meant that they could not be relied upon to prevent the German ships from putting to sea). They would also undertake additional minelaying in the Kiel Canal and the southern North Sea, while two squadrons of Coastal Command Beaufighters would be held back from patrols against E-boats. If the German force headed south, it was to be attacked by aircraft if the circumstances permitted, and also by light surface forces if it passed through the Straits of Dover in a bad visibility or at night.
Should the German fleet successfully run this gauntlet and break through the Straits of Dover, Operation HERMETIC would begin. Its aim would be to destroy the enemy warships before they could fall on the supply convoys running between Britain and France.
Admiral Ramsay would assume operational control in the Channel, while all build-up convoys at sea were diverted from the potential area of battle. The Vice-Admiral commanding at Dover would use his destroyers to locate, shadow and report the advancing enemy force. The Naval Commander, Eastern Task Force (Rear-Admiral Sir Philip Vian, Royal Navy) would take command of a force of battleships, cruisers and destroyers. These would come primarily from the British Eastern Task Force that was conducting Operation NEPTUNE, which would form Force H, ‘the main attacking force’ – detaching them from their vital role of providing fire support for the forces ashore to shift them temporarily back to their principal purpose. This force would be supplemented by warships from the American Western Task Force (designated ‘Force T’) as well as those held in reserve in Portsmouth – the battleships, and their escorts would be Force X, the cruisers and remaining destroyers Force Y. Vian’s fleet, comprising up to seven battleships and more than 20 cruisers, would come together at a buoy some 35 nautical miles south-east of the Isle of Wight, with fighter cover provided by 11 Group. The force commander was then ‘to proceed as necessary to bring the enemy to action’ – including an instruction that if gaining or maintaining contact with the enemy required entering known German minefields, he ‘should not hesitate’.
As it turned out, Operation HERMETIC was unnecessary; the German heavy ships did not sortie to challenge the Normandy assault or the subsequent operation to reinforce and sustain the liberation of western Europe. The existence of this plan, however, is a striking reminder of the continued albeit often overlooked role of major surface warships. In the era of submarines and land-based aircraft, capital ships were not sufficient to ensure the ability to use the sea, but they were still necessary. Even when they were not engaging their enemy counterparts, they remained the rock on which command of the sea ultimately rested.
This post first appeared at Defence-in-Depth, the blog of the Defence Studies Department, King’s College London.
Dr Tim Benbow studied at Oxford as an undergraduate (at Brasenose College) and as a graduate (at St Antony's College). He also spent a year at Harvard University as a Kennedy Scholar and a year at King's College London. After being awarded his doctorate he remained at Oxford, conducting a post-doctoral research project and teaching International Relations and Strategic Studies at the undergraduate and graduate levels, including one year as a Tutor in Politics at University College. Dr Benbow spent two years teaching at Britannia Royal Naval College, Dartmouth, before joining the Defence Studies Department in 2004. He was promoted to Senior Lecturer in 2008 and to Reader in 2016. Dr Benbow is Maritime Historian on the Higher Command and Staff Course; Deputy Director of the Corbett Centre for Maritime Policy Studies; and Director of the Strategy and Defence Policy Research Centre.