Submarines, however, were by no means the only danger faced by merchant ships of the English Navy. From the first week of the war, some were sunk or damaged by mines of a new type, with "magnetic influence", against which the English still had no response. However, on November 23, a German plane was to provide the solution. The plane dropped a mine in swamps off Shoeburyness. This mine was dismantled by Lieutenant Commander J.G.D. Ouvry, who took a very great personal risk but obtained, thanks to his exploit, the revelation of the polarity of this mine.
Strong with this discovery, the English were able to develop a magnetic dredger, capable of detonating these mines harmlessly. They were also able to equip the boats with a special system that allowed them to pass over the mines without triggering their detonator. Nevertheless, by the end of November, the magnetic mine had cost the English the loss of 46 ships—180,000 tons more. They also lost a destroyer which was sunk and several warships were damaged. By the end of 1939, total losses from the deadly mine amounted to 79 merchant ships, totaling 262,697 tons.
Another cause of casualties, even more difficult to combat, was the surface warship. It was mentioned above that, before the start of hostilities, the Germans had sent two "pocket battleships" across the Atlantic, accompanied by their resupply ships. A first hint of their presence in the ocean had been given to the Admiralty in the form of sunken or missing boats in waters far beyond those where U-boats used to prowl. The fact was to be confirmed as new losses were recorded. The Admiralty reacted by organizing hunting parties which were to cover the North Atlantic, the South Atlantic, as well as the Indian Ocean. On the other hand, cruisers and battleships were dispatched across the Atlantic to Halifax, Canada, to serve as escort and protect several convoys bound for England.
The first success, which was to boost English morale, was the destruction of the "pocket battleship" Graf Spee, in the Rio de la Plata estuary, off Montevideo, Uruguay. The Graf Spee had been tracked by the position of the ships it had sunk. He was chased, on the happy initiative of Commodore Henry Harwood, whose group, composed of the light cruisers Ajax, Exeter and Achilles, was in a favorable position to intercept him, while he was on his way to South America. , in search of new victims. It had sunk 9 English ships before being engaged in this operation, a mediocre result considering its overwhelming strength and firepower. The Deutschland expedition is even less fruitful. He managed to sink only 2 ships in the North Atlantic before being recalled by the mother country.
Deutschland's efforts were followed, in November 1939, by a more ambitious undertaking by from Admiral Raeder. He had sent the cruisers Scharnhorst and Gneisenau into the Atlantic, entrusting them with the mission of breaking up the English patrol lines. This preliminary operation was intended to give these two large ships a little experience before releasing them on the main English trade routes. They left Germany on November 21. On the evening of the 23rd, as they entered the Atlantic between Iceland and the Faroe Islands, they were spotted and attacked by the merchant cruiser Rawalpindi. The latter, of course, was no match for a big battlecruiser. She was quickly sunk by the Scharnhorst, having previously sent two reports to announce their presence.
Admiral Forbes, the Commander-in-Chief, immediately left Scapa Flow, with the Home Fleet , aboard the Newcastle, neighbor of the Rawalpindi on the patrol line. Approaching the scene of the encounter, he spotted the two cruisers, but lost track of them during a violent thunderstorm. Admiral Marschall, who commanded the two German ships, fled at full speed. He gave up the operation and returned to Germany. The Home Fleet then had little chance of overtaking it, because the distance which separated them was too great.
This maneuver was to give rise to some reservations in the minds of the British Admiralty as to the degree rigor with which the Germans conducted their businesses. It seems inexplicable that, having seen the Newcastle, the German cruisers did not turn against her to sink her. They could, with their powerful guns, overcome it quickly, and the fact of fleeing to regain Germany is incomprehensible. At that time, Admiral Forbes, as well as the Admiralty, believed that the Rawalpindi had been sunk by Deutschland. In any case, that does not explain this sudden about-face. Deutschland, too, had very powerful guns. This aspect of the German tactics was to be renewed during the hostilities, which each time did not fail to cause surprises.
At the very beginning of the operations, another part of the German plan proved that it had been miscalculated. This was the part of mobilizing forces in the North Sea to cripple a large number of English ships there. On December 12, 5 German destroyers, covered by 3 cruisers, made a sortie to lay a minefield off the coast of Northumberland. As they returned, they were spotted by the English submarine Salmon which torpedoed the cruisers Leipzig and Nürnberg, damaging them both. Two days later, as the latter approached the Danish coast, they were again attacked, this time by the submarine Ursula. The Leipzig was able to escape the torpedoes, but one of the destroyers accompanying her was hit and sunk.
For its part, the Royal Navy also knew its hard times. The harshest was brought to him early, on the morning of October 14th. U-47, commanded by Lieutenant Prien, managed to infiltrate the defenses of Scapa Flow, where it torpedoed the old battleship Royal Oak, which sank. The loss of this building proved to be of relative importance, given the power of the opposing navies, but what was serious was to realize that the main operational base of the Royal Navy was vulnerable to attack from the U-boat! Until its defenses could be reinforced by the services of a greater number of boats capable of blocking its entrances, the Home Fleet was obliged to use as a home port the port of Loch Ewe, on the west coast of Scotland, although this too was open to submarine attack. Sure enough, less than six weeks later, the fleet's flagship, the Nelson, was damaged by a mine while entering that port.
A comparative study, written at the end of 1939, would have, in terms of figures, proved favorable to the Royal Navy. The main question posed by the Admiralty, before the start of hostilities, concerned the threat posed to its maritime trade (and mainly its three large "pocket battleships") by German warships. The scales were already tilting in their favor since only 15 English ships, allied or neutral, had been sunk by them and only one of the three battleships was lying at the bottom of the ocean, in the harbor of Montevideo. The amount of the losses caused by the U-boats was not excessive either:114 ships of 421,000 tons had been sunk by them, of course, but, on the other hand, the English had destroyed 9 of them. (72 ships - 262,000 tons) were severe, but since the discovery of the polarity of the German magnetic mine, it was felt that this particular problem was solved. Of course, in the field of losses, one should also place that of the Royal Oak and that of the Courageous, as well as a merchant cruiser, 3 destroyers and a submarine, but, in total, this balance sheet was not too discouraging .
However, in the longer term, the Admiralty in London still had to face many problems. It had been believed, before the war - in fact, it was still believed since nothing had yet demonstrated the contrary, that the "asdic" detector, with which all anti-submarine ships were equipped, was a sufficient guarantee to avoid that the losses suffered between 1914 and 1918 are not renewed, especially after the discovery of the underwater grenade. As the importance of the building program undertaken by the Germans grew, the Admiralty expected that within a few years its defenses would be overwhelmed by the sheer weight of numbers, not to mention holes. which remained in the middle of the ocean and which left its convoys unescorted.
These concerns were to be confirmed during the first six months of 1940. The campaign in Norway, in April and May, as well as the evacuation of the English expeditionary force from the Channel ports, in May and at the beginning of June, are episodes known to the history of the war. A brief reference to these events is however necessary to show their repercussions on the whole of the defense of maritime commerce. During the Norwegian campaign, 10 destroyers and sloops were sunk. 14 others were damaged. During the evacuation of the expeditionary force, 6 other destroyers were to be sunk and 20 others damaged.
These losses represented a severe liability in the manpower of these boats which, by their nature, were the best escorts. The fall of France was to further aggravate the situation. The Channel coasts were now in German hands and rumors of an invasion were circulating. It was therefore necessary to blockade many buildings in the English Channel in order to monitor the movements of the enemy. This constraint, which lasted four months before the danger subsided, led, of course, to new and serious restrictions on the manpower available to escort merchant ships.
However, the worst was yet to come. In the last months of 1939, the Germans had tried, with quite relative success moreover, to organize attacks against convoys with the support of groups of submarines rather than engaging isolated elements. When a convoy was spotted and reported, the U-boat staffs would call out all nearby submarines to hasten the attack. From this initiative, it was easy for them to perfect this method. The U-boats were organized into "wolf packs". When the route of a convoy was sufficiently well identified, the nearest pack would rush to attack.
The submarine that had spotted the convoy was directing the rest of the pack using radio signals. No attack was undertaken until the entire pack arrived on the scene. To complete this tactic, night and surface attacks were inaugurated.
A submarine on the surface presents only a tiny silhouette, difficult to see, even in the best visibility conditions. It can also use its diesel engine, which makes it more maneuverable and faster than when submerged. In fact, the speed of a submarine on the surface exceeded that of most British escorts. There was, in these conditions, little chance of catching him, even if he had been spotted during the fight. Even more serious for the English was the fact that, on the surface, a U-boat was virtually immune to detection by asdic.
This completely changed the perspective with which enemy attacks on maritime commerce had been viewed before the war. The asdic and the depth charge were the foundations on which the whole theory of anti-submarine warfare had been based. The new German tactics completely foiled this theory. Nevertheless, the response was immediate:the escorts would be equipped with radars. The radar, in fact, could detect the presence of a submarine on the surface. But since no radar was available at that time, it took another whole year before the escort fleet could be equipped with it.
In the meantime, another task arose to the Royal Navy. At the time when the evacuation of the expeditionary corps from the Channel ports, and particularly Dunkirk, was being organized, troops were landed in France to prevent the advance of the Germans. But the situation was rapidly deteriorating on French soil. The hope of stopping this advance was very slim. It was even more so when it was realized that the defeatist elements of the French Government were in favor of negotiating an armistice with the Germans.
On June 15, it was decided to bring back to England the rest of the troops stationed in France. Most of them had only landed there a few days before. The ports of Cherbourg, Brest, Saint-Malo, La Pallice and Saint-Nazaire were to be used for this purpose. In the few days that this operation was carried out, 136,963 soldiers were repatriated, safe and sound, as well as 38,500 Allies, the majority of whom were Poles.
During this operation, there was only one loss to be deplored, but it was significant... Among the boats used to bring the troops back from Saint-Nazaire was the liner Lancastria. The latter was anchored in the port and had already embarked more than 5,300 soldiers when it was hit by the Germans during a violent air raid. She did not sink immediately, but 3,000 soldiers perished—simply because in the rush to evacuate, enough life belts could not be procured for all the excess men the liner had on board.
With the final withdrawal of British forces from French soil and the armistice that France had just signed with Germany, an entirely new problem presented itself to the Admiralty. The situation on which the first war plans had been conceived had now quite changed.
The Royal Navy had to take into account that the entire coast of Western Europe, from the North Cape in Norway to the Gulf of Biscay on the Spanish border, was in enemy hands. With the ports and bases of Norway in his clutches, Hitler could now dominate the eastern North Sea up to the Arctic Circle. This gave him a wide corridor, along which he could move his U-boats, his large battle-equipped merchant ships and his blockade runners into the Atlantic. With similar facilities in the Gulf of Biscay, submarines and other warships could penetrate deeper into the Atlantic before reaching areas where English ships were likely to board them. This made the task of the Admiralty infinitely more difficult, because nothing is easier for a ship than to hide in the vastness of the oceans.
An even more threatening danger to England's maritime trade was that the airfields of western France were occupied by the Germans. From there, the Focke-Wulf 'Condor' long-range aircraft could search the Atlantic, watching for British convoys, and signaling positions to submarines in ambush.
This problem particular was resolved in an improvised manner. Some merchant ships were fitted with catapults from which a fighter Hurricane could be launched. The most important convoys were accompanied by one of them when they had to pass within range of the Condors. If a Condor showed up on the horizon, the Hurricane would take flight, shoot down or deflect the intruder, and then make a forced landing near the ship that catapulted it so that its pilot could be picked up.
These merchant ships armed with catapults (they were called CAM-ships) paved the way, in their time, for MAC-ships (merchant aircraft carriers). The latter were merchant ships, usually tankers, because of their length, on which a flight deck had been fitted. MAC-ships could carry up to 6 planes which, naturally, could land on the deck after an operation at sea, instead of having to make this forced landing alongside another boat. Over time, the MAC-ships were replaced by auxiliary carriers (called "Woolworth"), which were merchant ships whose hulls had been entirely covered in order to transform them into real aircraft carriers.