Colin F. Baxter
East Tennessee State University

Abstract

For almost three years, from 1940 until the summer of 1943, German U-boats and Allied forces fought the greatest submarine campaign in history in the Battle of the Atlantic. During those desperate years, RAF Coastal Command suffered not only from a shortage of aircraft, but the aircraft that did seek out and find the enemy had no effective anti-submarine weapon to use against the U-boat. Only one U-boat “kill” is attributed to Coastal Command before 1942. It was commonly rumored in Coastal Command that its existing anti-submarine bomb could barely “rattle the wardroom crockery.” There were sound reasons for the Commander of the German submarine force, Admiral Karl Dönitz, to boast that an aircraft could no more sink a submarine than “a crow can catch and kill a mole.” And, while no single weapon, technology or tactic could replace the endurance of merchant seamen and sailors, the Torpex aerial depth charge finally provided RAF Coastal Command and Allied aircraft with a war-winning anti-submarine weapon.

Seven decades after World War II, the long, hard-fought see-saw campaign that British Prime Minister Winston Churchill called “the Battle of the Atlantic,” continues to be a subject of major historical interest, controversy and debate. ¹ Some recent writers have argued that while a few Allied convoys “suffered terribly,” most were “pretty safe” from U-boat (“U” being short for Untersee) attack. ² The World War II generation, however, had little doubt about the gravity of the threat to the Atlantic lifeline. Britain’s survival depended on importing large quantities of food, raw materials, machinery, and all of her oil. In February 1941 alone, Britain lost 400,000 tons of shipping, a rate of loss – 10 percent per convoy – that was unsustainable.  Moreover, unless the German submarine campaign was defeated, there could be no build-up of United States and Canadian forces in Britain for an invasion of German occupied Europe from the West.

Before the outbreak of World War II, British naval concern was focused on Germany’s powerful surface raiders rather than its small force of 18 ocean-going submarines. ³ Should a serious submarine threat emerge, as happened in World War I, the Admiralty were confident that the convoy system protected by escort vessels equipped with Asdic, an underwater echo-location device developed by British and French scientists between the wars, would manage the German submarine problem. ⁴ Once a U-boat was “locked in asdic’s grip,” the Royal Navy was confident its destruction would follow quickly from a “few well-placed depth charges.” ⁵

Under the conditions of war at sea, however, asdic quickly displayed serious limitations: it gave an approximate location of a submarine, but not its depth, and its range was only 1,500 yards. Asdic’s most serious defect was its inability to detect a surfaced submarine. Commander of the U-boats, Admiral Karl Dönitz, adopted the simple counter measure of having his U-boats, concentrated in a “wolf pack” of several boats, attack British convoys at night on the surface, where they could neither be seen by the escort lookouts, nor detected by asdic. ⁶ Early in the war, the odds of a submerged U-boat being sunk were also remote; the Royal Navy’s 450 lb. depth charges were filled with Amatol, a combination of ammonium nitrate and TNT, and were essentially the same as that used in World War I, with a lethal radius of only about seven yards. ⁷

A U-boat had even less to fear from RAF Coastal Command aircraft, since their role was primarily that of naval reconnaissance. ⁸ The Royal Air Force had been divided into three Commands in 1936, and Coastal Command had to compete for scarce resources, first with Fighter, then Bomber Command. ⁹   In the inter-war years, no one wanted to repeat the trench-war bloodletting of World War I, and the bomber offered an offensive alternative to a major land war.  With the defeat of the French Army in 1940, and at the height of the Battle of Britain, Winston Churchill declared, “The Fighters are our salvation, but the Bombers alone provide the means of victory.” ¹⁰

Coastal Command’s main anti-submarine weapon in 1939 was the feeble 100 lb. bomb. ¹¹ In December 1939, a Coastal Command aircraft mistakenly attacked HMS Snapper, which was on the surface. ¹² The aircraft scored a direct hit on the base of Snapper’s conning tower, causing total devastation – to four of the electric light bulbs in Snapper’s control room. ¹³ Air Marshal Sir Philip Joubert, who commanded RAF Coastal Command for 17 months during World War II, recalled in his memoir that the 100 lb. anti-submarine bomb was commonly reported to have broken nothing but the “ward-room crockery when one fell by accident on one of our own submarines!” ¹⁴ In the years 1941 until 1943, historian Correlli Barnett noted that RAF Coastal Command remained “a sea bird, weak on the wing, short of sight and blunt of beak.” ¹⁵

At a meeting of the Air Ministry Bombing Committee in December 1939, it was agreed that the explosive RDX, which had been developed at the Woolwich Arsenal, would make the anti-submarine bomb more powerful, but the supply of the new explosive was inadequate for this purpose. ¹⁶ Air Marshal Sir Frederick Bowhill, then Chief of RAF Coastal Command, made “vigorous demands” for more lethal weaponry, but a completely new weapon might take two years to perfect; that was far too long. ¹⁷ The only other British anti-submarine weapon available, however, was the drum-shaped naval 450-pound depth charge. ¹⁸ The normal brief of the First Lord of the Admiralty was to protect the budget and political interests of the Royal Navy; however, Winston Churchill, who would not become Prime Minister until 10 May 1940, wasted no time on turf battles in seeking to provide RAF Coastal Command with a naval depth charge. In a letter marked “Urgent,” the energetic First Lord asked Admiral Bruce Fraser, the Controller of the Navy: “One of the aeroplane Squadrons on the East Coast would like to have a depth charge in order to test effects on flight, speed and dropping. There is no need to supply a loaded depth charge. Will you kindly make available for Commander Anderson RAF sometime tomorrow a depth charge case, empty, together with a statement of the weight with which it should be filled, so that experiments can be made [with the depth charge] . . .  Commander Anderson will call for it and take it to his Squadron.” ¹⁹  

In August 1940 Coastal Command obtained 700 depth charges from the Admiralty.  These weapons, however, did not prove to be the solution to Coastal Command’s armament problem. Lacking an efficient bombsight, aircraft crews were forced to attack from such a low level that they risked damage from the explosion of their own depth charges. ²⁰ When a smaller 250-pound Amatol filled anti-U-boat depth bomb was introduced, it was found to be “not powerful enough for its job.” ²¹                                                            

At sea, merchant ship losses were alarming; during 1940 over a thousand ships were sunk, totaling 4 million tons, a quarter of British merchant shipping.  At this rate, Germany could win the war by simply starving Britain of supplies. In 1939, those imports amounted to 68 million tons; by 1941, the figure had dropped to 26 million tons. Against these dangerous losses, few U-boats were being sunk. ²² In an effort to breathe new life into the floundering anti-U-boat campaign, on 6 March 1941, Prime Minister Churchill used a striking phrase to describe the naval campaign that threatened to sever the Britain’s Atlantic lifeline, naming it “the Battle of the Atlantic.” To promote increased inter-service cooperation, the Air Ministry and the Admiralty agreed that RAF Coastal Command would be under the operational control of the Admiralty. ²³ The tug-of-war between the Air Ministry and the Admiralty over strategic priority, however, was never settled to the satisfaction of both sides.

In June 1941, Air Marshal Sir Philip Joubert became head of Coastal Command for the second time; his own favorite post, if not his most successful command. ²⁴ Prior to the appointment, Joubert had been Assistant Chief of the Air Staff (Radio) at the Air Ministry, and it was hoped that he would improve the input of technology in the aerial maritime war. ²⁵ RAF historian Denis Richards wrote that, “The new Coastal chief was determined not to rest until the aeroplane was thoroughly lethal to the submarine.” ²⁶

On the initiative of Joubert, Professor Patrick Blackett was posted to Coastal Command, where he became Joubert’s scientific adviser. ²⁷ Within a few months of joining Coastal Command, Blackett had collected a group of young civilian scientists to form an Operational Research Section (ORS), which used scientific analysis to recommend tactical changes. ²⁸ One of the first scientists Blackett brought in to work with him at Coastal Command was Professor E. J. Williams who “jumped right away” into the question of why Coastal Command aircraft were sinking so few U-boats? ²⁹ depth charges sank any U-boats.” (127).]

Williams’s analysis of Coastal Command attacks on U-boats up to May 1941 showed that out of the 215 attacks, only two enemy submarines were sunk, or a success rate of only 1 percent; that 2 ½ percent were “probably sunk,” and 15 percent suffered some damage. ³⁰ Williams reported that a partially visible or just submerged U-boat was about ten times more vulnerable to aircraft attack than one that had been out of sight for 15 seconds, and that changing the existing depth charge setting from 100 feet to 25 feet or just below the surface, together with narrowing the stick spacing between bombs, would increase the percentage of U-boats “kills” by an “astonishing” factor of ten – from the current 1 or 2 percent to 10 to 20 percent. ³¹ Williams also noted that improved camouflage of aircraft on anti-submarine patrol would tend to reduce the proportion of U-boats that escaped detection by submerging. ³²

At the first meeting of the Admiralty Anti-Submarine Warfare Committee, in the summer of 1941, Williams’s report was accepted, and as a first step, the depth charge setting was changed from 100 to 50 feet. ³³ The ORS scientists believed that this was still too deep, and as new fuses became available the settings were changed to 25 feet. ³⁴ Not until the summer of 1942 was the 25 feet depth setting in general service. Blackett would write after the war that, “Captured German U-boat crews thought that we had introduced a new and much more powerful explosive . . . Actually we had only turned a depth-setting adjuster from the 100-foot to the 25-foot mark.” ³⁵ Blackett attributed the “spectacular results” to “a small and simple change in tactics.” ³⁶ He believed that, “too much scientific effort has been expended hitherto in the production of new devices and too little in the proper use of what we have got.” ³⁷ At the time, however, Blackett pressed for the adoption of the new explosive Torpex.     

The U-boat prisoners-of-war, however, were not mistaken in thinking that the British had introduced a new and more powerful explosive than amatol.  Torpex (short for TORPedo Explosive), a combination of RDX, TNT, and aluminum powder had replaced the amatol filling in the 250-pound aerial depth charge. The deadly cocktail increased the weapon’s underwater power by about 50 percent. ³⁸ The ORS pressed for urgent action to be taken by Air Chief Marshal Joubert to obtain RDX, the critical ingredient of Torpex. ³⁹ In September 1941, Joubert asked the Air Ministry for a supply of RDX. ³⁹ Within a week, the Air Ministry replied that Minol, a lower grade explosive, could be supplied, but not RDX. ⁴¹ Air Chief Marshal Joubert replied to the Air Ministry offer in the strongest terms:

We are much exercised at the feebleness of the explosive in our depth charges.  The lethal distance is so small as to make kills practically unobtainable. I hear that there is a new explosive called “Torpex” (not repeat not Minol) which weight for weight is 50% better than our present explosives and volume for volume 75% better.  It seems to me therefore of the greatest importance to have our depth charges filled with Torpex since it would greatly increase our chance of getting kills. Will you, as a matter of urgency, look into this and see what can be done. ⁴²

Air Commodore J. D. Breakey, at the Air Ministry, responded that “the advantage of Torpex over Minol would not, in fact, be large,” and that “RDX, which is the main ingredient of Torpex is, as you know, only available in small quantities.” ⁴³ Breaky noted moreover that diverting RDX to Coastal Command for use in Torpex would necessitate taking RDX from other purposes, “such as the 500 lb. M.C. [medium capacity] bomb, which was specially designed for RDX filling.” ⁴⁴ RAF Coastal Command’s request for RDX came at a time when RAF Bomber Command was anxious to replace their largely ineffective high explosive Amatol bombs with the new explosive, which was “obviously the best choice but was not readily available in 1941 in large quantities.” ⁴⁵ “You will be glad to know,” wrote Breakey, “that everything possible is being done to increase the supply of RDX . . . We have also brought the maximum political pressure to bear on the U.S. authorities to adopt and manufacture this explosive. No substantial increase, however, is likely to be practicable for at least twelve months since the erection of a special plant is involved.” ⁴⁶ Breakey noted in a postscript that Torpex had been discussed at an afternoon meeting of the Admiralty’s Anti-Submarine Warfare Committee, and “Nobody at this meeting had precise figures as to its [Torpex] efficacy.” However, he declared that “the Admiralty appear to have been sufficiently satisfied on this point to divert a sufficient quantity of their supply of RDX to fill 260 of the 250 lb. depth charges per month.” ⁴⁴

Air Chief Marshal Joubert had also sent a copy of his letter requesting Torpex to Air Commodore Patrick Huskinson, the Director of Armament Development at the Ministry of Aircraft Production (M.A.P.). ⁴⁸ Huskinson’s reply was noncommittal. ⁴⁹ He agreed that “Torpex is the best filling available for the purpose,” but questioned the 50 percent superiority figure cited for Torpex, compared to the “35 percent improvement usually associated with Torpex.” ⁵⁰ Huskinson doubted the accuracy of both figures, quoting information he had received from the Submarine Mine Division (S.M.D.): he stated that “S.M.D. has informed this Directorate that too much reliance should not be placed on these figures as they are based on a few small scale shots,” and that more tests were needed before a reliable figure was obtained. ⁵⁰   “Unfortunately,” said Huskinson, he was “unable to arrange supply [of RDX],” adding, “I have no doubt that if they [the Admiralty] agree with the urgency of the requirement there will be no difficulty in arranging diversion of a portion of the present Admiralty supplies to [Coastal Command] depth charges.” ⁵⁰

Joubert forwarded a copy of Huskinson’s reply to Patrick Blackett “to see & comment.” ⁵⁰ In January 1942, Blackett had moved from RAF Coastal Command to the Admiralty, and started building up an operational research group to deal with naval matters.  Blackett’s comments were forthright and blunt: “The letter from D. Arm. D. [Huskinson] is rather misleading, I think.” ⁵⁴ Citing data contained in Huskinson’s own letter, Blackett wrote that, “It follows that by refilling a 250-pound depth charge with Torpex one will get 75% more explosive energy. This will bring the equivalent TNT value of the charge to 288 lbs., i.e. very nearly up to that of the 450-pound depth charge.” ⁵⁵ An outspoken critic of the bombing campaign against Germany, Blackett declared:

I rather suspect that D. Arm.’s letter was actuated, possibly unconsciously, by the wish to write down the value of Torpex for A/S [anti-submarine] work, so as to avoid attempts to steal RDX from RAF bombs!

It was agreed by D. A/S.W.’s [Director, Anti-Submarine Warfare] Committee on Wednesday that D.T.M. [Directorate of Torpedoes and Mining] shall start filling 250 lb. depth charges with Torpex almost immediately, but the Navy has only available enough Torpex to fill about 260 250 lb. depth charges per month.  This would keep Coastal Command going, but is quite inadequate to build up distributed stocks. It does seem very important to try and get some extra RDX released as a non-recurrent supply to enable reasonable stocks of Torpex filled depth charges to be built up. I feel very strongly that the Air Ministry ought to be pressed again and again to release some of their supply destined for their big and beautiful bombs. ⁵⁶

Reinforced by Blackett’s comments, Joubert returned to the attack. He informed Huskinson, “I want to return to the charge on the subject of Torpex for A/S work.” ⁵⁷ He told Huskinson that the Director of Technical Material had agreed to fill 250 lb. depth charges with Torpex almost immediately, but there was only enough available to fill about 260 250 lb. depth charges per month. ⁵⁸ Since that number was about Coastal Command’s monthly consumption, Joubert declared that, “we shall never be able to build up a stock.” ⁵⁸ If Huskinson could let Coastal Command have a two months’ supply of Torpex, wrote Joubert, “Once this is agreed we shall not be entrenching on Bomber Command’s requirements again.” ⁵⁸

The Senior Air Staff Officer at RAF Coastal Command, Air-Vice Marshal G. B. A. Baker, also pressed the need for Torpex. In a letter to Air Commodore G. A. H, Pidcock, who had replaced Huskinson as Director of Armament Development at the M.A.P., Baker wrote that, “Submarine attack is perhaps one of the most difficult for obvious reasons. The target is small, fleeting and of great value. It is rarely chanced upon—once in the tour of duty of an anti-U-boat crew on the average.” ⁶¹ What they wanted, he wrote, was “(a) greater accuracy of aim (b) greater bomb effect.” ⁶² Baker had been told by Coastal Command’s ORS that the average bombing error from the point of attack was 60 to 80 yards. ⁶³ As to greater bomb effect, “both the C-in-C [Joubert] unofficially and the Command officially have written stressing our claims for consideration for Torpex or even for submarine strafing, and D/A.S.W. [Director of Anti-Submarine Warfare on the Admiralty’s Naval Staff, Captain G. E. Creasy] is in full support.” ⁶³ Baker extended an invitation to visit Coastal Command Headquarters at Northwood: “I wonder if you could find the time to come out to lunch here one day – it is only 40 minutes away.  I think it would interest you to see our problem and also to discuss with the R.A.F. and Naval Staff our present feelings as to what is required to solve it.” ⁶⁵ “All congratulations on your new job,” Baker wrote to Pidcock.

The Northwood meeting took place on 13 February 1942, but Huskinson took the place of Pidcock. Huskinson had been appointed liaison officer between M.A.P. and the various RAF Commands. ⁶⁶ Sir Ralph Sorley, Assistant Chief of the Air Staff (Technical), also attended the Northwood meeting, where Joubert again took the opportunity to press Coastal Command’s case for Torpex. ⁶⁷ Sorley agreed to approach Bomber Command with regard to the release of RDX on the basis that Coastal Command’s requirements were very small, and the targets “both important and fleeting.” ⁶⁷ Previously, Huskinson had earlier questioned the underwater effectiveness of Torpex, but at Northwood, “He strongly repudiated the suggestion that the under-water effect of Torpex was less than that in air.” ⁶⁷ After discussing the anti-U-boat problem with the Naval Staff, Huskinson “undertook to impress on those concerned at the Air Ministry and Ministry of Aircraft Production the importance of this work and of having the best possible weapons to carry it out.” ⁷⁰

In spite of these encouraging words spoken at the Northwood meeting, the Torpex supply was viewed as an Admiralty problem, and not an Air Ministry one, a point made clear in a letter that Huskinson wrote to Air Vice Marshal Baker at Coastal Command (Baker had continued to press for Torpex) only three days after the meeting. Huskinson wrote, “I have spoken to Sorley again today and asked him to expedite the Admiralty, as this is entirely a supply question.” ⁷¹ Huskinson emphasized that, “I want to stress that it is entirely A.C.A.S. (T)’s [Sorley’s] funeral to force the Admiralty into action.” ⁷²

Captain George Creasy, the highly capable Director of Anti-Submarine Warfare at the Admiralty, was also kept informed of RAF Coastal Command’s efforts to obtain Torpex from the Air Ministry. ⁷³ Creasy completely agreed with Baker, and replied that there was every prospect of getting enough Torpex to fill not only the “Hedgehog” for surface ships, but the 250-pound depth charges for aircraft. ⁷⁴ Creasy wrote:

I know you will appreciate that I fully share your keenness to hot up the potency of the aircraft charge. I am absolutely convinced that had we had the 25 ft. setting and the higher efficiency explosive over the past six months we should have been able to count a large proportion of the ‘Seriously Damaged’ U-boats as in the bag. ⁷⁵

In the meantime, Coastal Command continued to lack a lethal anti-U-boat weapon. A frustrated Air Chief Marshal Joubert, in a letter to the Air Ministry, explained his Command’s lack of an effective anti-U-boat weapon, and requested a new and bigger bomb to replace their existing weapon:

For the entire duration of the war, to date, we have been attempting to attack U-boats with two types of depth charges neither of which is capable of giving us satisfactory results. We started off with the standard Admiralty Mark VII depth charge, and we have made many attempts to make this a satisfactory aircraft weapon. Despite all attempts to improve it, it has now been found impossible to clear the Mark VII depth charge for dropping from heights about 150 feet and speeds above 150 knots . . . it was therefore found necessary to design a special small 250 lb. depth charge, the Mk. VIII.  This weapon has been satisfactory from the point of view of tactical use, since it is not restricted in height or speed; but recent experience of attacks upon U-boats have proved conclusively that its killing power [amatol filling] is quite inadequate, and that it is seriously impeding the effect of our anti-submarine warfare as a whole.

We therefore require that a special aircraft depth charge should be developed on the highest priority and to the following specifications. ⁷⁶

Joubert went on describe what was required, namely a 500-pound, Torpex filled depth bomb that was capable of being dropped from heights up to 5,000 feet and speeds up to 200 knots. ⁷⁷ The requested aerial depth bomb eventually became the 600-pound depth bomb.

Joubert’s decision to request a big anti-submarine bomb came a month before the first batch of 250-pound Torpex filled depth charges were delivered to RAF Coastal Command squadrons with the best attack records. ⁷⁸ By June 1942, Coastal Command was receiving 150 a week, or 600 a month. Air-Vice Marshal Baker explained to Creasy, however, that Coastal Command had a “very difficult problem” keeping sufficient Torpex depth charges available at the Stations where they were needed most.” ⁷⁹ “I hope you will not think that I am flogging a dead horse,” he told Creasy, “indeed I know it to be a live one although it is not galloping fast enough.” ⁸⁰ In a follow-up to a telephone call, Creasy replied:

As you know we have had a long battle to obtain any RDX for Torpex filling for the Navy in the past.  The whole supply went to the RAF. We eventually obtained half the output.  This allowed us to fill Hedgehog projectiles for our ships, and Mark XI Torpedoes, and 600 Mark VIII depth charges per month for aircraft. ⁸⁰    

Creasy told Baker that they had made such a strong case “at last Thursday’s meeting of the RDX Committee” that out of a total output of 260 tons per month, “210 tons had now been allocated to the Navy, 30 tons to the R.A.F., and 20 tons to the Army.” ⁸⁰ As a result, they could increase the output of Torpex aerial depth charges to 3,000 per month. “Thus all your troubles with shortage-of Torpex depth charges should cease shortly,” promised Creasy. ⁸⁰ He was confident that they could soon start supplying Torpex depth charges to the outlying stations, the Middle East, Far Eastern area, and West Africa. ⁸⁰ Creasy said that Canadian output was expected to start soon, and that the Canadians would probably be able to fill their own Torpex aerial depth charges. ⁸⁰

The good news concerning Torpex came too late for Joubert in whose eyes the weapon had been discredited by its failure to dramatically increase U-boat kills. His hopes were now placed in the development of a new and bigger anti-U-boat depth bomb. He acknowledged that the 250-pound weapon had brought “some improvement” in the lethality rate to 6 percent, but “it had been hoped confidently that at least 20 percent ‘kills’ would result.” ⁸⁶ Joubert argued that the change in depth setting from 100 to 25 feet “was probably at least as effective [as Torpex], since the “majority of attacks were made when the target was only just below the surface.” ⁸⁷

Joubert’s disappointment with the 250-pound Torpex aerial depth charge is apparent in his August letter to the Admiralty’s new Director of Anti-Submarine Warfare, Captain C.F. Clarke (Creasy had taken up a sea command): “I continue to be more and more disappointed with the results of the 250-pound Torpex aerial depth charge. Many attacks have been made during the last few months and very little indication has been seen of damage to the enemy.” ⁸⁸   Joubert’s and the Air Staff’s skepticism of the 250-pound Torpex-filled depth charge was not without justification, since the overall lethality of air attacks on U-boats was still disappointingly low. At the end of 1942, the lethality rate was 7 percent, not the hoped for 20 percent.

In his letter to Captain Clarke, Joubert wrote that he had heard that one of their own submarines [HMS Talisman] while on the surface, had been attacked by one of their aircraft, “apparently quite accurately, and that the submarine was able to proceed to the Mediterranean quite undisturbed.” ⁸⁹ Joubert continued, “It is obvious that the 250 lb. depth charge is a most unsatisfactory weapon, and that before we can achieve any real success against the submarines we must find the right answer.” ⁹⁰ He told Captain Clarke that he had also seen the results of tests with the 35 lb. hollow-charge bomb – a weapon strongly supported by Lord Cherwell – and he was prepared to try it as an alternative weapon. ⁹¹ Nevertheless, he thought the weapon was “only really suitable for our smaller aircraft and that we should press on with the utmost vigor with the production of the 600 lb. A/S (Anti-Submarine) bomb, for which we have been asking these many months.” ⁸⁹

The small “hollow-charge bomb” that Joubert referred to was the small A/S bomb advocated by Lord Cherwell, a weapon described by the Operational Research Scientist as    Lord Cherwell’s “baby” which he attempted “to sell to Coastal Command.” ⁹³ Statistical data, however, did not support Cherwell’s proposal.

In his reply to Air Chief Marshal Joubert, Captain Clarke agreed that after some air attacks, the U-boat had apparently got away, but he had every reason to expect that considerable damage had been done to the submarine, and that “there have been some kills.” ⁹⁴ Clarke believed that the Torpex depth charge, with 36 feet spacing, and a 25 feet depth setting, was lethal to a surfaced U-boat, provided the weapon fell accurately across the center of the target. ⁹⁵ Regarding the attack on Talisman, Clarke reported that the submarine was at a depth of 47 feet, and that the Torpex aerial depth charges had fallen across the stern at right angles to the track.  As a result, wrote Clarke, “The damage, although not lethal, was by no means undisturbing . . . requiring at least 14 days to make good the repairs.” ⁹⁵ Clarke did agree with Joubert that with increased bombing accuracy the 600-pound depth bomb should prove a good weapon.” ⁹⁵

In early September, Joubert received word from the Admiralty’s Anti-Submarine Warfare Committee making it clear that Torpex was unavailable for a 600-pound depth bomb. ⁹⁸ Joubert strongly protested the decision in a letter to Sir Henry Tizard who was scientific adviser to the Air Ministry. He explained that the new 600-pound depth bomb was required as a replacement for the Torpex depth charge, which he said “had proven to be ineffective unless practically a direct hit were obtained. ⁷⁷ Joubert wrote to the First Sea Lord, Admiral Sir Dudley Pound, “almost despairingly, about the state of the anti-submarine war.” ¹⁰⁰ “Unless some radical change in the rate of destruction takes place,” wrote Joubert, “we are faced with an ever increasing fleet of U-boats at sea.” ¹⁰⁰

Joubert and the Air Staff argued that the 250-pound Torpex weapon “did not have a lethal radius of anything like the 19 feet claimed by the ORS, and pressed that priority be given to the 600-pound depth bomb.” ¹⁰² The 19 feet lethal radius of the Torpex weapon was a figure called in question at various times, but an assessment made in 1944, and based on photographic evidence, showed a possible lethal radius of 42 feet for two Torpex depth charges straddling a U-boat hull. But the Air Staff favored a larger bomb, and “bitterly accused” the scientists of paying no attention to the “big bang” of a larger bomb, even if it failed to damage the U-boat. ¹⁰³ Was the 250-pound Torpex weapon at fault for the failure to score more U-boat kills or was the problem with the inaccuracy of the attacks, which depended on “pilot’s eye bombing”? ORS insisted that the “overwhelmingly most important problem” was to improve anti-U-boat bomb aiming. ¹⁰⁴ The scientists further argued that in the excitement of an actual attack the accuracy of bomb release was likely to be well below that achieved under practice conditions. ¹⁰⁵

“Faithful to their own kind,” Joubert and the Air Staff, accepted the aircraft crews’ figure of a bombing error of only about 20 yards. ¹⁰⁶ For Joubert to have blamed poor pilot bomb aiming or inaccuracy would have reflected badly on his own air crews, and he may have genuinely believed in the accuracy of their reports.  Later reports showed that bomb aiming errors were far greater than expected by the Air Staff.  Most attacks were some 60 yards ahead of the conning tower. Development of a low level bombsight significantly reduced the bomb aiming error, thus increasing the lethality rate per attack. ¹⁰⁷

Historian Christina Goulter has noted that no Operational Research Scientist was present at the meeting when the decision was made to proceed with the 600-pound depth bomb, and that Joubert “came close to sinking his Command’s anti-submarine effort” by advocating the [600-pound] bomb rather than the [250-pound Torpex] depth charge as the prime weapon. ¹⁰⁸ Later analysis of photographic evidence supported the position of the ORS that most of the 250-pound Torpex depth charges were dropped, not on the U-boat’s conning tower as intended, but about 60 yards ahead of the target. ¹⁰⁹ The accumulation of photographic evidence allowed the ORS to carry out more refined analysis of attacks, which led to improvements in stick (a group of bombs released to fall across the target in a straight row) length and stick spacing. ¹¹⁰ The Operational Research Scientists also made great efforts to develop an effective low level bomb-sight, which was finally introduced early in 1944. ¹¹¹ C. H. Waddington concluded that the decision to proceed with the development of the “big bang,” 600-pound anti-submarine bomb was “almost certainly a mistake.” ¹¹²

Once it was recognized that bombing accuracy was not as high as the aircrew had thought, practice bombing on the training range became far more rigorous. On-the-job training was hardly possible for RAF Coastal Command crews when an attack on a U-boat was a rare event (typically one attack in 500 hours of flying time) in the life of an aircrew. ¹¹³ But with increased training, and yet more practice on the bombing range, together with improved tactics, the lethality of the Torpex aerial depth charge increased. Between July and December 1942, Coastal Command aircraft sank 15 U-boats – in the words of historian John Terraine, “it was definitely in the game.” ¹¹⁴ Monthly Coastal Command reports graphically confirmed the rising “kill” rate against the U-boat:

On 15 September 1942, a [Whitley] Coastal Command aircraft flying at 6,700 feet, sighted a U-boat at a distance of 7 miles. It was making ten knots.  The aircraft turned and broke cloud at 3,000 feet, then attack from the U-boat’s port quarter with five Torpex depth-charges released from 20 feet while the U-boat was fully surfaced.  The depth-charges straddled it; three fell short to port, one made a direct hit on the bridge, and one fell beyond to starboard . . . The aircraft turned to make another attack . . . The remaining Torpex depth charge exploded in the center of this oil and debris, 5 seconds after the bows had gone out of sight. . .

The crew of the Coastal Command aircraft reported that total destruction of the U-boat was “more than likely.” ¹¹⁵ They were correct: post-war investigation showed that the attack marked the end of U-261. ¹¹⁶ A pilot and armament expert who served in Coastal Command explained the difference made by Torpex: “By the time I arrived in Iceland we were using a Minol and then a Torpex filling, with much more shattering force than the other two [Amatol and Minol].  But for its [Torpex] presence in the 250-pound D/C [aerial depth charge], we could never have begun at long last to sink U-boats.” ¹¹⁷

In October 1942, Squadron Leader Terrence “Bull” Bulloch of No. 120 Squadron, flying a B-24 Liberator, sank U-597 south-west of Iceland. Bulloch dived to attack from the U-boat’s port quarter and dropped six Torpex depth charges from 75 feet while the submarine was still on the surface: “The U-boat was completely covered by the stick [of Torpex depth charges], both in line and range, from bows to stern.” ¹¹⁸

After 17 months as head of Coastal Command, many of them intensely frustrating – the only response to his requests to the Air Ministry seemed to be “No” – Joubert was succeeded by Air Marshal Sir John Slessor in February 1943. ¹¹⁹ The previous year, 1942, had been the worst year of the war for the Allies in the Battle of the Atlantic.  Merchant ship sinkings in the Atlantic reached 5.4 million tons; total Allied losses reached 7.8 million tons, or 1,662 ships sunk. ¹²⁰ Knowledge of U-boat movements had been lost in February 1942 when the Allies lost their newfound ability to read German Enigma signals (the decoded signals were called Ultra). This intelligence black-out lasted until the end of the year. Without Ultra decrypts of U-boat Command’s signals to its submarines in the Atlantic, routing convoys to avoid U-boats was extremely difficult.  Moreover, Dönitz now had enough U-boats spread across the Atlantic to allow several wolf-packs to attack many different convoy routes. The rate of loss was devastating to the British. ¹²¹ British imports dropped to one-third of their pre-war level; by January, 1943, the British navy had only two months’ supply of oil left. Small wonder that Prime Minister Churchill later wrote, “The only thing that ever really frightened me during the war was the U-boat peril.” ¹²²

But before the Atlantic battle reached its climax in the spring of 1943, both sides had to endure another North Atlantic winter of gale force winds, mountainous icy seas, and driving blizzards that pounded both sides without mercy. Once the worst of the winter weather was past, the fiercest battles of the Atlantic campaign began. One of the biggest battles occurred in mid-March when 40 U-boats attacked two convoys, sinking 22 merchant ships totaling 141,000 tons for the loss of just one U-boat. ¹²³ Admiral Dönitz, forewarned by the German Navy’s intelligence division, B-Dienst (which read British convoy cyphers), had stationed wolf-packs across the path of the two convoys. In a period of 20 days, no fewer than 70 Allied ships, or half-a-million tons had been sunk in the North Atlantic. Victory appeared to be within Dönitz’s grasp.

With seeming suddenness, however, the tide turned in favor of the Allies. With Ultra intelligence once again able to provide timely information, a considerable number of convoys had been steered clear of U-boats altogether. ¹²⁴ And by 1943, the problem of accurately locating U-boats had been solved by fitting both aircraft and convoy escorts with centimetric radar that could detect surfaced submarines at ranges of four or more miles, day or night.  Many escorts were also equipped with HF/DF (High Frequency Direction Finding), nicknamed Huff-Duff, which could intercept short-wave radio transmissions to and from a U-boat, thus provide the bearing and range of the boat transmitting. B-24 Liberators, equipped with centimetric radar, could detect a surfaced U-boat at five miles. At night, as the aircraft flew closer to a U-boat and lost radar contact, the aircraft’s searchlight, known as the Leigh Light, was switched on trapping the U-boat in its glare. Once detected, U-boats now faced formidable attack from aircraft and escort vessels that were manned by better-trained air and naval personnel.

German submarine crews felt more and more helpless as Allied aircraft attacked without warning to smother their boat with “a devastating pattern of 250 lb. [Torpex] depth-charges.” ¹²⁵ In May, 41 U-boats were sunk by aircraft, 16 of them by Coastal Command. ¹²⁶ One U-boat was now lost for 10,000 tons of shipping, compared to one U-boat to 100,000 tons just a short time previously. By the end of the May, Admiral Dönitz had lost 30 percent of his U-boat force. Appalled by this catastrophic rate of loss, Dönitz reluctantly ordered withdrawal from the North Atlantic. It was intended to be temporary, but U-boats never again seriously threatened the Atlantic supply line. By June 1943, Allied shipping losses fell to the lowest figure since the United States had entered the war: 21,754 tons in the Atlantic.  Between June and December 1943, only 57 ships were sunk in the Atlantic for the loss of 141 U-boats. In 1944, the Allies lost only 31 ships in the Atlantic compared to 1,006 in 1942. At this stage of the war, such shipping losses were more than replaced by the prodigious production of American shipyards.

Air Chief Marshal Sir Charles Portal, Chief of the Air Staff, extended his “admiration and warmest thanks” to Coastal Command for their “brilliant success,” which was the result of “tireless perseverance and devotion to duty.” ¹²⁷ Fortunately, for both aircrews and aircraft, they now carried a weapon that could destroy more than a submarine’s light-bulbs or wardroom crockery.

A final opportunity for critics to replace the 250-pound Torpex depth charge with the 600-pound depth bomb came in the Bay of Biscay when Coastal Command aircraft again attacked the U-boats’ routes across the bay. Dönitz decided that it was best for his commanders to abandon the “crash-dive” tactic, and instead to stay on the surface and fight enemy aircraft with their anti-aircraft weapons. ¹²⁷ In July and August, about 11 percent of Coastal Command aircraft were shot down. ¹²⁹ At one point in the summer of 1943, the Command was losing an average of one aircraft a day in the Biscay area. ¹³⁰ In his memoirs, Slessor recalled, “In Whitehall [the Air Ministry] there were long faces and prophets of gloom.” ¹³¹ The critics of low level attacks with the Torpex depth charge pointed out how British fishing trawlers, in the early days of the war, once they were armed, had driven-off the Luftwaffe. ¹³¹ It seemed quite possible that low level day attacks would become too expensive, and if that was the case, the obvious remedy was to attack from a high altitude using the 600-pound depth bomb. ¹³³ These views met with “no sympathy from Slessor.” ¹³⁴ In spite of RAF Coastal Command’s losses, there was a steady increase in the deadliness of their attacks on visible U-boats. Between July and October 1943, the lethality rate per attack was 30 percent. ¹³⁴ For U-boat crews, each mission was more and more likely to be their last. ¹³⁶

By 1943, there was little or no doubt that Coastal Command possessed a lethal airborne weapon. Air Marshal Slessor described the Torpex depth charge in these terms:

The decisive weapon of the anti-submarine squadrons was the Mark XI Torpex depth charge, dropped in ‘sticks’ of four to eight from point-blank altitude, fifty to a hundred and fifty feet. There were others . . . There was the 600 lb. special anti-submarine bomb, designed to be dropped from higher altitudes . . . which only accounted for one U-boat in 1943 . . .  But they were none of them comparable as U-boat killers with the old Mark XI depth-charge.  It had its earlier critics; but if the depth-setting was right, if the distance between the depth-charges making up the ‘stick’ was properly spaced, above all if crews were well trained and laid their ‘sticks’ accurately, it was an exceedingly effective weapon, as the figures show. ¹³⁷

By the end of 1943, RAF Coastal Command aircraft armed with the Torpex depth charge had sunk an impressive 84 U-boats, out of 219 U-boats that were destroyed in that decisive year. ¹³⁰ The 600-pound depth bomb “only accounted” for one U-boat in 1943—U-462. ¹³⁹ By the end of the war, Coastal Command had dropped 97 in 28 attacks compared with 5,790 of the Torpex depth charges in 1,170 attacks. ¹⁴⁰ The lethality of Coastal Command attacks on visible U-boats had risen to over 45 percent. ¹⁴¹

Beginning World War II with the virtually useless 100-pound anti-submarine bomb, Coastal Command attacks on U-boats remained ineffective until the introduction of the Torpex aerial depth charge in the summer of 1942. By May 1943, all the pieces necessary for Allied victory in the Battle of the Atlantic were put into place. And, at long last, Coastal Command, possessed a vastly more powerful anti-U-boat weapon in the Torpex aerial depth charge.  At a decisive point in the Atlantic battle, Torpex helped ensure that 1943 would be a “bumper year” for the Allies in the six-year war against the U-boat.    

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Footnotes