During November 1942 Admiral Sir Percy Noble, who had been C.-in-C., Western Approaches since February 1941, was succeeded by Admiral Sir Max Horton. Starting with miserably inadequate resources, Noble had done a magnificent job in creating a viable AS defence for the convoys. Churchill, however, found him lacking sufficient aggression, wanting a man who would use the Allies’ growing strength to carry the war to Dönitz. In Horton he made the perfect choice. A career submariner, he had been in command of the whole Royal Navy submarine force and well understood Dönitz’ problems and weaknesses. Horton was ferocious with erring subordinates yet knew that the war against the U-boat was one of patience, for which the maintenance of morale was top priority. In pursuit of this he regularly sailed on operational cruises and flew with Coastal Command crews.
First Wellington variant to be developed specifically for Coastal Command was the GR. VIII, a general reconnaissance/torpedo-bomber version of the Pegasus XVIII-engined Mk IC. Equipped with ASV (Air to Surface Vessel) Mk II radar, it was identified readily by the four dorsal antennae and the four pairs of transmitting aerials on each side of the fuselage. A total of 271 torpedo-bombers for daylight operation was built at Weybridge, together with 65 day bombers, and 58 equipped for night operation with a Leigh searchlight in the ventral turret position. In these last aircraft the nose armament was deleted and the position occupied by the light operator.
There was, however, still an important role for the Wellington to play with Coastal Command. Maritime operations had started with the four DWI Wellingtons: these had been converted by Vickers in the opening months of 1940 to carry a 52-ft (15.85-m) diameter metal ring, which contained a coil that could create a field current to detonate magnetic mines. Eleven almost identical aircraft, with 48-ft (14.63-m) rings, were converted by W. A. Rollason Ltd at Croydon, and others on site in the Middle East.
No. 172 Squadron at Chivenor, covering the Western Approaches, was the first to use the Leigh Light-equipped Wellington VIII operationally, and the first attack on a U-boat by such an aircraft at night took place on 3 June 1942, with the first sinking recorded on 6 July. From December 1941 Wellingtons were flying shipping strikes in the Mediterranean, and in the Far East No. 36 Squadron began anti-submarine operations in October 1942.
The Coastal Command of the RAF, which was eventually to prove such a potent obstacle to Dönitz’ plans, enjoyed a painfully slow expansion. Until early in 1941, invasion was the primary threat to the nation. In denying the Luftwaffe the necessary air supremacy for such an undertaking, Fighter Command took an indisputable top priority. Bomber Command, with its deeply ingrained strategic bombing theories, could equally claim that it alone could strike directly at the enemy, reducing his capacity to continue the war through the destruction of his industrial base and the morale of his populace.
In July 1940, as Dönitz’ boats extended their range by beginning operations from Biscay bases, Coastal Command had 500 aircraft, but only thirty-four of them were Sunderlands, capable of operation beyond a 500-mile radius. The enemy increasingly operated at the fringe of these limits.
Further to the all-important anti-invasion patrols, there were others to watch for attempted breakout by raiders, and the establishment of an AS reconnaissance line running north-westward from Cape Wrath. Patrols were gradually set up on a regular basis from Iceland, and then from Freetown, the busy southern terminal of the SL convoys.
For nearly two years, poorly equipped and lacking experience, Coastal Command spent thousands of hours patrolling, seeing U-boats aplenty but sinking none except in support of surface AS escorts. Then, on 27 August 1940, they captured one. With what appeared to be the most incompetent crew that ever sailed, the U-570, a Type VIIC, surfaced south of Iceland almost beneath a patrolling Hudson. Four shallow-set depth charges caused extensive superficial damage and created panic. With the boat unable to dive, the aircraft kept the crew below with strafing runs until further aircraft and, eventually, the Navy arrived. With some difficulty, the U-570 was recovered and repaired. Although all sensitive material had been destroyed, the boat provided valuable operational data when re-commissioned with a Royal Navy crew.
Slowly, Coastal Command accumulated new aircraft – Sunderlands and Catalinas, Beaufort torpedo bombers, Blenheims and the new Beaufighter. As Bomber Command expanded its four-engined, heavy bomber fleet, it passed down some still-useful twin-engined aircraft – Hampdens, Whitleys and the versatile Wellington.
The useless AS bombs had been superseded by depth charges, modified for air drop but yet lacking a reliable ultra-shallow fuse. As U-boats were usually attacked while on or near the surface, this was an urgent requirement. To evaluate new weapons and to establish correct attack procedures a Development Unit was created.
Although the ASV Mark II, the first practical air-to-surface radar set, was introduced in August 1940, Bomber Command took first priority. When the development of the magnetron oscillator then facilitated a high-power centimetric radar, the discovery was shared with the Americans, who began production of sets with trainable antenna but small enough to be airborne. For these, Coastal Command’s priorities ranked below those of the night fighters of Fighter Command.
Radar gave an aircraft the ability to surprise the U-boat, surfaced at night to recharge batteries and to refresh on-board air. Unfortunately, like Asdic-equipped ships, the aircraft was ‘blind’ over the very last stage of the approach, as the synchronously-switched transmitter and receiver units could not cope with near-simultaneous returns.
The solution was the brilliantly simple ‘Leigh Light’, a 24-inch naval projector mounted in a turret ring and controlled by the standard gun mounting servo system. When trials began in March 1941, a Wellington was required to accommodate the associated generator, but later variants were powered from a bank of trickle-charged accumulators. Entry into service of a device so important was inexcusably slow, it seeing action for the first time in June 1942.
From the middle of 1941, U-boats commissioned at an increasing rate while mercantile losses fell off considerably. This false dawn led to demands that Coastal Command’s heavier aircraft be diverted to assist in Bomber Command operations. But this was to ignore that these same aircraft were a major reason for the improvement. Air cover extended some 700 miles westward from the British Isles, 600 miles eastward from Canada and 400 miles southward from Iceland. Within these limits, surfaced U-boat skippers found that they could be caught with little warning. Around the fringes life was safer, for the longer-range aircraft remained scarce and could not dally so far from base. The U-boats correspondingly congregated in what was known as the Gap, an aircraft-free zone, several hundred miles in width, occupying the central one-third of a line drawn from Iceland to Newfoundland. The Admiralty’s Submarine Tracking Room thus sought to use intelligence to direct convoys in a great northerly arc, to avoid known submarine concentrations and to remain a maximum time within the limits of air cover.
Noting the decrease in interceptions, Dönitz initiated the first of several inconclusive enquiries to establish whether naval codes had been compromised, how to reduce the number of radio transmissions and to evaluate the accuracy of the known British D/F system.
By the end of 1941 a first Coastal Command squadron was converting to the American-built B-24 Liberator. This aircraft proved vulnerable as a daylight bomber over the Continent but was remarkably successful when converted for long-range maritime patrol duties, being well able to cover the Gap.
As the Bay of Biscay had to be traversed by every U-boat leaving or returning to its French base, it was divided into sectors by Coastal Command. These sectors reached down to Spanish coastal limits and each was covered in a planned patrol programme. Submarines increasingly had to submerge during daylight hours, slowing their progress and reducing their endurance.
Mid-1942 saw the strength of RAF Coastal Command stand at over fifty flying boats (Catalinas and Sunderlands) and nearly 500 other aircraft. These included Hudsons, Wellingtons, Whitleys and Hampdens for general reconnaissance but only two squadrons of B-24 (Liberator) and B-17 (Fortress) Long Range Maritime Patrol aircraft. As the Luftwaffe was now operating Ju88 and Me110 heavy fighters over the Bay of Biscay, there were also deployed eight squadrons of Beaufighters and the more vulnerable Blenheims.
In addition, four naval squadrons were attached to the Command, together with specialist units for photographic, meteorological and air-sea rescue duties. Based around the British Isles (with Group headquarters at Liverpool, Chatham, Rosyth and Plymouth), at Iceland and Gibraltar, the Command’s aircraft were complemented by those of the US Navy and the Royal Canadian Air Force (RCAF) operating from Iceland, Newfoundland and the Canadian mainland. Despite increasing offensive capacity, however, the Gap yawned as wide and as deadly as ever.
With the reduction in scale of submarine attack, it became the practice to reduce the degree of evasive routing and to follow more closely the shortest Great Circle routes. There came also an inevitable relaxation in vigilance, so that it came as an unpleasant surprise when Dönitz set up the occasional pack attack. This he did in order to prevent the transfer of escorts to assist the beleaguered Americans.
One such attack fell on HG.84, a twenty-three ship convoy which sailed northbound from Gibraltar on 9 June 1942. Barring its route were the nine U-boats of Group Endrass, named for the ‘ace’ lost in these waters some six months earlier. The group itself contained one ace skipper in Erich Topp of U-552. It was he that had earlier sunk the American destroyer Reuben James and, by virtue of surviving the war, would accumulate a ‘score’ of 185,000 GRT, earning him the Ritterkreuz with Oak Leaves and Swords.
By coincidence Endrass’ nemesis, Captain F.J. Walker, was again the Senior Officer of the escort, although EG.36 was at a reduced strength of Walker’s sloop Stork and three Flowers. Included in the convoy was the fighter catapult ship, Empire Morn.
Enemy agents in Spain duly reported HG.84’s departure. Twenty ships sailed from Gibraltar, the final three joining from Lisbon on 11 June. These were tracked by Kondors, which thus discovered the main convoy. The reported position proved to be thirty-five miles in error, prompting a tart comment from Dönitz.
With the convoy’s slow progress, Dönitz was able to deploy his boats in two search lines and it was Topp himself that made the first sighting on the afternoon of the 14th some 400 miles west of Cape Finisterre.
In vectoring-in the three colleagues, Topp generated radio traffic that was noted by the rescue ship Copeland at the rear of the convoy. Rescue ships did not enjoy any special immunity and were equipped with ‘Huff-Duff’, the existence of which was suspected by the enemy but not yet confirmed. The Copeland alerted Walker who ordered away the Empire Morn’s solitary Hurricane to disperse the snoopers while his four escorts pursued three separate contacts.
With darkness, Topp had worked himself into an attacking position. He launched a full, four-tube bow salvo, then swung to fire the stern tube. Three ships went down, the Norwegian tanker Slemdal and two British ships, Moss Hutchinson’s Etrib and MacAndrew’s Pelayo. Reloading rapidly, he was able to repeat his attack, this time destroying two Ellerman ships, Hall Line’s Thurso and the Papayanni vessel City of Oxford. The four British ships aggregated barely 8,500 GRT but typified the valuable little Mediterranean traders which, working cargo with their own equipment, could use the most minor ports.
Despite the number of boats in contact with the convoy by the 15th they were kept at a safe distance by the escort, Topp and one other receiving sufficient damage to cause them to break off.
On the following day the escort was reinforced by three fresh ships, including two of the new River-class frigates. The convoy also came within the range of Coastal Command Liberators. Continuous air cover and calm conditions caused the remaining enemy to abandon the operation. Topping-up from a pair of U-tankers, they resumed their interrupted passage to the United States.
That the enemy was thus being ‘let off the hook’ was of great concern to the Admiralty which, as soon as suitable vessels could be mustered, initiated the Support Group concept. This comprised an independent group, accompanied by its own oiler, which could be directed to reinforce the escort of any threatened convoy. First tried in September 1942, the idea immediately faltered with the need of every available ship to cover the North Africa landings in the November. Requirements here consumed not only every possible AS escort but also the first escort carriers (CVE) that were coming forward. It was thus a further six months before Support Groups would become a reality, for which reason the Admiralty initiated the emergency Merchant Aircraft Carrier (MAC) programme. This, however, would produce no result before May 1943.
Deployment of escort carriers pitted U-boats against that most unlikely of killers, the Fairey Swordfish. Often portrayed as an obsolescent stopgap, the aircraft was nothing of the sort, having entered service with the Fleet Air Arm only in July 1936. Designed to handle well at very low speeds, it could lift off a short flight deck with a relative wind speed of only 55 knots. A rare example of a successful multi-purpose design, the Swordfish could deploy torpedoes or mines, and even engage in divebombing in the face of light opposition. Fitted with ASV radar, it carried depth charges or, later, hull-piercing rocket projectiles, to deadly effect against submarines. Often ‘superseded’, it nevertheless remained operational throughout the war.
Although ASV Mark II radar had first been flown in March 1941, Fighter Command’s night fighters enjoyed higher priority than Coastal Command, and it was June 1942 before the enemy became convinced that his surfaced submarines were being surprised because of airborne radar rather than poor watch-keeping. In this same month came a further alarming report of a U-boat, surfaced at night in the Bay of Biscay, being surprised by a sudden illumination and almost simultaneous bombing. The Leigh Light had arrived.
From their French Atlantic bases, all U-boats had to deploy and return across ‘the Bay’ and the growing attentions of Coastal Command were a matter of concern to BdU. Where early 1942 had been casualty-free, June had seen three boats damaged sufficiently to abort their deployments and return. Unusually, Dönitz over-reacted, ordering boats to remain submerged at night, surfacing by day only to recharge and refresh. This was intended to be only a stopgap measure, pending the improvisation of a suitable radar warning receiver. Its result, however, was to more than double the number of sightings and to begin a slow attrition as odd boats were picked off.
Following complaints about lack of Luftwaffe cover, two dozen fighter versions of the Ju88 were transferred to Lorient and Bordeaux. Additional automatic weapons began to appear on U-boats, starting a trend to growing topside clutter that had a cumulative and adverse effect on surfaced stability and submerged manoeuvrability.
Ironically, a couple of French firms, Metox and Grandin, were already producing electronic equipment which, with the addition of a crude antenna, could receive signals over a bandwidth that included the frequency range of ASV Mark II. Known simply as ‘Metox’, the first sets were rushed to completion within six weeks. On surfacing, boats so equipped would hoist a wooden-framed antenna (the ‘Biscay Cross’) and submerge again hastily on the reception of a train of signals at around 200 MHz. Metox-equipped boats escorted those without and, once again, sightings dropped almost to zero.
With their superior electronic industrial base, the Americans were keen to apply technology to AS warfare. Airborne magnetic anomaly detectors were shown to work in principle but the distance from detector to the ferrous mass of the target could not exceed 600 feet. Even the lowest and slowest of aircraft could thus detect a transient lasting only milliseconds.
Expendable air-dropped sonobuoys appeared to be more promising. Released around a suspected target position, these detected target noise, amplified it and re-transmitted it to the circling aircraft. By the end of 1942 they were in use by both US Army Air Corps and US Navy aircraft, and were about to go into mass production.
As sonobuoys could give only an approximate position for the target, precision-dependent weapons such as depth-charges were not appropriate. For this purpose, the self-homing acoustic torpedo was developed. For submarines, too, this was a useful weapon for, launched against a threatening escort, it allowed a skipper to concentrate on a convoy. The Germans had been working on the device since 1933 but progress had been slow. Targeting depended upon matched pairs of sensitive and highly-directional hydrophones. As these, in a fast torpedo, would be swamped by self-generated noise, the weapon was electrically-propelled at about 25 knots. Wrongly assuming that the Allies were already using acoustic torpedoes, German scientists managed to deploy them operationally during 1943.