ANTONY PRESTON, JOHN BATCHELOR
THE SUBMARINE SINCE 1919
Once more, Germany was attempting to strangle Britain's supply lines with an all-out submarine campaign. But while the outcome was never certain, time was against the U-Boats. Experienced commanders could not be replaced, and the manpower and materials shortage affected the U-Boats as much as any other branch of Germany's armed forces. For the second time they would come within sight of victory, and for the second time they would be denied it
A Mosquito bomber armed with rockets attacks a diving submarine
By the end of 1940 many U-Boats had been moved to the French Atlantic ports, with 12 flotillas based on Brest, La Rochelle, La Pallice, St Nazaire, Lorient and Bordeaux. Being so much nearer to the Western Approaches and the North Atlantic gave them greater operating time, and so made them far more effective than before. For the same reason, when the Italian Navy offered some of its submarines to the Germans for use in the Atlantic it was decided to base them on Bordeaux rat her than make them travel all the way from the Mediterranean.
The first Italian submarines to make a passage of the Straits of Gibraltar were the Giuseppe Finzi and Pietro Calvi in June 1940. After further attempts had shown how difficult it could be, owing to the currents in the Straits, the Italian Naval Staff decided to embark on the expense of setting up a permanent base at Bordeaux, and this was begun in August 1940. It came to be known as BETASOM, from Beta (= "B" for Bordeaux), and Som (= Sommergibili), and by January 1941 the base was able to cater for 27 submarines. This massive effort would have been very helpful to the Germans, but for the fact that the design of the Italian submarines proved so poor. They had prodigiously large conning towers, some of which were equipped with a galley and a lavatory for the comfort of watchkeepers, but had only modest surface speed.
BETASOM did its best to remedy the defects, and many desirable features of the German U-Boats were incorporated when possible. The main patrol area was off the Azores, and in the 2,5 years in which Italian submarines operated they sank almost 1 million tons of Allied shipping, or an average of some 31,000 tons sunk by the 32 boats involved. When the Italians tried to make a separate peace in 1943, two of the surviving boats at Bordeaux were seized by the Germans and taken into the Kriegsmarine as UIT21 and 22 (UIT stood for U-Italian).
As soon as the German base facilities were ready Admiral Dönitz switched to the attack once more. In August 1940 Hitler declared a total blockade of the British Isles, thus freeing the U-Boats from the restrictions that had been in force since the beginning of the war. Success did not come easily, for the growing skill of British escorts made coastal waters too dangerous for the U-Boats, and so they had to move out westwards. Here they found the going easier, and between June and November 1910 losses of shipping rose to nearly 1,600,000 tons. Fortunately the United States replaced its "Cash and Carry" legislation with an agreement to "lend" war equipment, particularly 50 old but useful destroyers, in exchange for a 99-year lease on various bases throughout the British Empire.
The "bases for equipment" exchange had little immediate effect on the U-Boat war as the destroyers took some time to be refitted as anti-submarine vessels, but it put heart into the British when they most needed it. It also depressed the Germans, who felt that America was once more trying to rob Germany of her rightful victory, and many senior Nazis urged Hitler to declare war on the United States before she could re-arm and rescue' the British. But the Germans had their own problems, particularly in maintaining an adequate number of U-Boats at sea. Surprisingly little equipment from the navies of Europe had fallen into German hands, despite the swift collapse of resistance in May and June; dockyards were wrecked and although some captured submarine hulls were salvageable it would take months before they could be put back into service. The building programme had been stepped up, but like other branches of the armed services, the U-Boat Arm had been equipped for a short war, and pre-war planning for expansion had been unrealistic.
Only four U-Boats were launched between the outbreak of war and the end of 1939, and a further 60 followed in 1940. But in the same period British air and surface forces had sunk 32, and accidents had increased the total to 34. This was a much heavier loss rate than the U-Boats had sustained in the early years of the First World War, and proved that the British convoy escorts were skilled opponents. The withdrawal of destroyers from escort duties to meet the threat of German invasion after Dunkirk had denuded the convoys to a dangerous extent, and although the U-Boats scored more kills than ever before, there were only about thirty at sea at any moment, too few to exploit their enemy's weakness. This was the period of the great U-Boat aces, like Prien and Kretschmer, and some of them sank the staggering total of 200,000 tons of shipping apiece, an achievement which earned them the award of the Knight's Cross with Oak Leaves.
The aces soon found that a night attack on the surface made a U-Boat almost invulnerable. The British escorts' Asdic could not detect a surfaced submarine, and it took an exceptionally sharp lookout to spot the conning tower of a U-Boat. Kretschmer went a step further, and took his U-Boat inside the columns of the convoy, the last place an escort commander would think of looking, and from this "sanctuary" he could sink ships with impunity while his torpedoes lasted. The answer to this tactic was surface- warning Radar, but in 1940 no escorts were fitted with it, so merchant ships were fitted with illuminant rockets known as Snow- flakes; when these were launched at the orders of the escort commander any U-Boat near the convoy would find itself suddenly exposed to view.
It was at this time that Admiral Dönitz began to intervene more directly in the conduct of U-Boat operations. Realising that the exploits of the aces could not be emulated by the newer submarine commanders and crews, he was anxious to use the large numbers of new boats in "wolf packs". The essence of the wolf pack tactics was the swamping of a convoy and its escorts by a co-ordinated attack from a group of U-Boats. To achieve this a U-Boat which made contact with a convoy was given strict orders not to attack but to signal its course and position to U-Boat Headquarters, which would then make contact with other U-Boats in the area and direct them to the original U-Boat's position. When the pack was assembled it was launched against the luckless convoy in a series of night attacks, night after night if necessary.
The chief danger from wolf pack tactics was that a U-Boat was both fast and hard to detect on the surface. Running at 17 knots on her diesels, a U-Boat could outpace the trawlers, corvettes and sloops which made up the bulk of convoy escorts in 1940 and 1941. Destroyers were faster, but too few. and in any case the lack of a radar set in all but a few ships made it difficult for any escort to sight a U-Boat. The new tactics were introduced between October 1940 and March 1941, and they proved deadly.
Another factor contributing to their success was the aerial reconnaissance provided by Focke-Wulf Condor aircraft operating from French airfields. These four-engined aircraft were able to locate convoys and shadow them for the benefit of the U-Boats, and until air-cover could be provided for convoys there was virtually no defense against them.
As stated before, the small size of the Type VII U-Boats prevented them from ranging too far in pursuit of targets, and to offset this a "U-tanker" was introduced. The Type XIV was known to the Germans and the British as the "Milch Cow", and each one could carry 432 tons of spare fuel and four torpedoes for transfer on the surface. Only ten were completed in 1941/42, and as Allied anti-submarine forces were told to give them top priority all were sunk. A further ten were cancelled because the growing threat from aircraft made refuelling on the surface too dangerous. For the same reason a series of much larger supply boats, the Types XV and XVI were also cancelled.
Italian Brin. The 1,000-ton Brin Class of four boats were completed in 1938, but a year later another two were added to replace an earlier pair transferred to General Franco during the Spanish Civil War. Armament: Eight 21-in torpedo-tubes (forward); one 3·9-in gun; four 13·2-mm machine-guns. Speed: 17·4 knots (surfaced), 8·7 knots (submerged)
The British adopted several counter-measures to meet the new threat. In May 1941 the first Type 271 surface search radar set went to sea in a corvette, and as it could detect a conning tower at 2,5 miles or more it put paid to surface attacks at night. Another device was High-Frequency Direction-Finding, known for short as Huff-Duff or H/F-D/F. Its principle was well known, but the British had been able to produce a set of great sensitivity which was small enough to be installed in an escort, and this meant that the vital signals sent by a shadowing U-Boat could be traced to within a quarter of a mile. The result was that the U-Boat could at least be forced to dive, and thus silenced; an immediatealteration of the convoy's course then gave the U-Boats the lengthy task of relocating the convov and re-assembling the wolf pack.
March 1941 was a bad month for the U-Boats. Five U-Boats were sunk in the North Atlantic, including the three aces Prien (U47), Kretschmer (U99) and Schepke (U100). A month later U110 fell into British hands for long enough to allow boarders to recover her code-books. The results of this exploit was good enough for the Admiralty to keep its secret until well after the end of the Second World War. Even today it is not known exactly how much knowledge of German cyphers was gained, but it can be assumed that some of the successes against U-Boats in 1941 were attributable to the capture of U110.
There was no quick answer to the Focke-Wulf Condor, but an interim remedy was to fit some merchant ships with a catapult for launching a single Hurricane fighter aircraft. Although there was no way of recovering the fighter, it was a fair exchange for the degree of immunity conferred on the convoy if the shadower was shot down. Ideally each convoy needed its own aircraft carrier, but in 1941 this was quite beyond the Royal Navy, even if there had been sufficient aircraft to equip the carriers.
The other area in which improvements were made was weaponry. The difficulty in holding a submarine contact with Asdic as the contact came closer to the searching ship has already been mentioned: the answer was to provide a weapon which could project bombs or depth-charges ahead of the ship, while she still held the U-Boat in the Asdic beam. Development of such weapons took time, and in the meantime it was only possible to increase the number of depth-charges which could be dropped. Before the war two depth-charge throwers and a short rack of charges was considered enough, but by 1941 most escort destroyers had surrendered a gun on the quarter-deck for a heavy outfit of four throwers and two extended racks of depth-charges. Better reloading gear was provided so that an escort could keep up a continuous attack, and the pattern of dropping charges was revised to give the maximum chance of destruction.
The standard Mark VII depth-charge had already been modified for use in aircraft, but it was also made heavier to make it sink faster. This was an attempt to reduce that gap between the time the Asdic beam lost contact with the U-Boat, and the explosion of the first charge; obviously the shorter the time interval the more precise was the attack. Another more deadly weapon was the Mark X depth-charge, a 15-ft long canister packed with Minol, one of the new explosives developed during the war. This 1-ton monster could only be fired from a torpedo-tube, and when it exploded at great depth its concussive effect produced damage over a greater radius. It had its drawbacks however: being the equivalent of a full pattern of ten ordinary depth-charges it could blow the ship's stern off if set too shallow or if the ship was moving too slowly.
In 1941 the first "Hedgehog" appeared. This was a spigot mortar for firing 24 small bombs well ahead of the ship in an elliptical pattern. Each bomb had a 32-lb charge of Torpex (another new explosive) and a hit from one could sink a U-Boat. It allowed the firing ship to hold the target in the Asdic beam, but unlike the ordinary depth-charge a near miss did no harm at all to the U-Boat. In 1943 the British produced a fearsome weapon called "Squid", which fired three full-sized depth-charges ahead of the ship, and thus combined the advantages of both the earlier weapons.
To be on the receiving end of these weapons was a harrowing experience. For a start there was the audible "pinging" of the Asdic, and then if a searching escort gained contact would come the repeated concussion of patterns of depth-charges, each one containing 300 lb of high explosive. Light bulbs were shattered and small leaks could be started in the pressure hull. These were particularly dangerous as the mixture of seawater with the sulphuric acid in the batteries generated chlorine gas, which attacks the mucous membranes of the breathing passages.
A prolonged attack could keep the U-Boat down until her air-supply was exhausted even if she had not suffered structural damage. Evasive action was difficult because the noise of the electric motors could be detected by the enemy. If a submarine was trapped by a number of escorts and kept down until her air-supply ran out the choice of options was not inviting: to stay down and die of asphyxiation or blow tanks and try to fight it out on the surface.
Other ideas were germinating. At the end of 1941 the British converted a small merchant ship, the ex-German banana boat Empire Audacity into the first "escort carrier", HMS Audacity. She carried only six Martlet fighter aircraft, which had to be parked aft on her small wooden flight deck as there had been no time to provide a lift or hangar. The purpose of this conversion was to provide a defense against the Focke-Wulf Condors which were causing a great deal of trouble to the convoys running from the British Isles-to Gibraltar, but it proved that small utility aircraft carriers were a possibility. Audacity served for only a month before she was torpedoed off Portugal during a fierce convoy battle, but her aircraft had made so much difference that more conversions were ordered.
The entry of the United States into the war in the same month changed the whole situation, for she alone could provide the numbers of aircraft and the building resources to convert more escort carriers. As a result of strenuous British entreaties six mercantile hulls were converted in April and May 1942, and five of them were immediately transferred to the Royal Navy. However, the Americans were badly equipped for anti-submarine warfare, despite their decisive intervention in 1917, and the first result of their entry into the war was merely an inflation of the losses of merchant shipping. The U-Boats moved over to the Caribbean and the East Coast of the United States, where they found so many juicy targets that they christened the early months of 1942 the "Happy Times". It took only 21 U-Boats to sink 500 ships in six months.
The Americans' unpreparedness cannot be blamed on surprise, for the US Navy had been escorting ships bound for the British Isles to a "Mid-Ocean Meeting Point", called MOMP for short, since September 1941. One destroyer had been sunk and another severely damaged by U-Boat torpedoes during this quasi-war, and the British had freely handed over information about their anti-submarine measures. Furthermore, the Admiralty had ordered 50 American-designed escorts early in 1941.
How was it, then, that the US Navy appeared to have no way of protecting shipping in its own coastal waters? The answer is that senior officers still doubted the wisdom of convoys, even after all experience had shown how vulnerable unescorted ships were to submarine attack. The Americans, having a large number of elderly destroyers, and no specialised escorts like the British sloops and corvettes, pinned their hopes on "hunting groups", or high-speed patrols by destroyers to seek out the U-Boats before they could attack. It was seriously held by some officers that convoy was too defensive a measure to appeal to the aggressive American spirit - it might suit the more dogged, patient British but it was too old-fashioned an idea to be used by dynamic Americans.
Of course this argument had been the one used by the British from 1914 to 1917 to justify their own "aggressive" tactics, and it ignored the inescapable fact that it was impossible to cover the ocean with patrol vessels. The submarine by virtue of its invisibility need only hide until the patrolling group had passed, and this is just what happened. During the "Happy Times" U-Boat commanders reported that they could almost set their watches by the American patrols, which signalled their approach by plumes of smoke and impressive bow waves as a squadron of destroyers tore past at 30 knots. Once past, the length of their patrol line ensured that they would not be back for some time, and the U-Boat could rely on a free hand in running down solitary merchantmen once more. Furthermore security was bad, the American coastline was ablaze with lights, and the merchantmen chattered to one another in plain language, giving their positions regularly. Under these circumstances it is hardly surprising that 505 ships (nearly a third of the total for the whole year) were sunk in American waters before June 1942, when the US Navy finally organised all shipping into convoys.
German "Milch Cow" Type XIV. To extend the range of the Type VII U-Boats, the German Navy built ten submarine tankers in 1941. With a fatter and shorter hull than the Type IX boats, and less power, they could carry sufficient fuel to keep four or five U-Boats at sea for twice as long as usual, and they also carried four spare torpedoes in external stowage. They were made top priority targets for Allied ships and all ten were sunk. Displacement: 1,688 tons (surfaced). Armament: Two 37-mm AA guns; one 20-mm AA gun; no torpedo-tubes
Galling though these losses were, the British and Americans were able to coordinate their counter-measures very well. The programme of 50 British destroyer escorts (BDEs) was hurriedly expanded to 250, and further designs were put into mass-production, so that eventually over 1,000 hulls were on order by 1943. As an emergency measure, Lend-Lease was put into reverse to allow 25 "Flower" Class corvettes to be transferred to the USN, and the new British escort design, the "River" Class frigate was put into production in American yards. But convoy proved to be the essential measure once again, and when introduced brought the shipping losses back under control.
Not that the position of the Allies was anything but alarming. In 1941 Great Britain had lost a total of 4,328,558 tons of shipping, representing 1,299 ships in all; U-Boats had sunk over 2 million tons (432 ships) while surface raiders, aircraft and mines accounted for the rest. But in 1942 the U-Boats alone sank over 6 million tons, while the total losses from all causes amounted to 7,790,697 tons (1,664 ships). It was April 1917 all over again, except that this time all possible counter-measures had been put into effect and yet the U-Boats were winning. In January 1942 the Germans had 91 U-Boats operational, and although 87 were lost during the year, new construction meant that 212 were operational by December.
The scent of victory
Dönitz and his submarines could smell the scent of victory in the air, and he exhorted them to greater efforts. It was essential for the U-Boats to prevent the Americans from bringing their enormous resources to bear on Europe, and Dönitz calculated that it would take a monthly loss rate of 800,000 tons of Allied shipping to starve out the British and prevent the Americans from implementing their strategic plans to liberate the Mediterranean and the Continent of Europe.
The average monthly losses of shipping in 1942 were running at 650,000 tons, which was far beyond the rate of replacement, so the first priority for the United States was to build more merchant ships. With boundless ingenuity and energy American shipyards devised methods of mass-producing ships, and soon "Liberty" and "Victory" standard hulls began to appear in numbers. The British were beginning to see the results of their large warship-building programmes of 1940/41, and in 1942 the first "River" Class frigates appeared, 1,400-ton twin-screw ships with enough endurance to cross the Atlantic and more speed than a surfaced U-Boat. With more radar sets and H/F-D/F sets available for escort vessels the existing convoy escorts were also better equipped to fight off wolf pack attacks, and this was reflected in the large number of sinkings in 1942.
The U-Boats were helped at this time by the so-called "black gaps" in mid-Atlantic, five areas which were out of range of shore- based aircraft. In these areas U-Boats could stalk convoys without the fear of being forced to dive by an aircraft, and they sank many ships with little loss to themselves. The introduction of more escort carriers in the late summer of 1942 and the provision of a handful of VLR (Very Long Range) Liberator bombers helped to close the air gap, but the numbers of both would remain small until 1943.
A useful interim measure was the MAC-ship or Merchant Aircraft Carrier, which was an oil-tanker or grain-carrier equipped with a plywood-flight deck to allow her to operate four aircraft. The virtue of this compromise was that it did not prevent the ship from continuing to carry her valuable cargoes, whereas an escort carrier was completely gutted and converted to a warship. On the other hand an escort carrier operated from 15 to 24 aircraft, and had the . necessary communications equipment for controlling aircraft over a convoy.
The U-Boats continued their grim War of extermination, for their goal of 800,000 tons of enemy shipping sunk per month seemed within reach. Indeed Admiral Dönitz believed that they had reached the magic figure, but as in the First World War, U-Boat commanders tended to over-estimate the tonnage of their victims. As we have seen, the losses did not exceed 650,000 tons, which meant that the collapse of the Allies was further away than Dönitz thought. New torpedoes and devices were coming forward, and it was hoped that these would tip the scale. The most important were the homing torpedo and a radar impulse detector, the torpedo to increase the rate of hits and the detector to reduce the chances of being surprised by ship or aircraft on the surface.
The first homing torpedo was issued in January 1943, and was known as the T4 or "Falke", but after only thirty had been used it was replaced by the better-known T5 "Zaunkonig". This was the weapon known to the British as the "Gnat" (for German Naval Acoustic Torpedo), and it travelled at the relatively low speed of 25 knots to reduce interference from its own noise.
Two factors combined to frustrate the Allies' efforts to beat the U-Boat offensive in 1942. The first was the Americans' virtual withdrawal of their escort forces from the Atlantic in June 1942, because these were needed for the Pacific against the Japanese. The second factor was the need to earmark escorts for the large convoys which would be needed for the invasion of North Africa, "Operation Torch". Although they were still responsible for coastal escort work, the American ships retained in the Atlantic now formed 2 per cent of the escort forces available, with the British and Canadians sharing the burden in a 50:48 ratio. This dilution of effort was unavoidable, but it gave the U-Boats a chance to inflict even heavier losses than they might have done, when the escorts were at full stretch.
To counterbalance this problem the large number of escort vessels coming into service did allow the British to organise the first experimental support group in September 1942. This was a group of escorts which operated independently in search of U-Boats, but kept itself at readiness to go to the aid of a hard-pressed convoy. It should not be confused with the old-style hunting groups, because it was based on the convoy system rather than being a replacement for it. The basic idea was to leave the convoy's escort to look after the close-range defense, while the support group could pursue and harry U-Boats to destruction. All too frequently a convoy escort had to leave ii promising contact because she had to return to the convoy, and the support group idea promised to increase the number of sinkings. This is exactly what happened, particularly because support groups were able to operate in the areas where U-Boats were concentrated.