Blackett's War (41 page)

Several more weeks of analysis and discussion among Blackett’s group produced some further insights into what was going on. A convoy’s size made almost no difference in the chances that the convoy would be sighted and attacked by a U-boat. It also made almost no difference in the absolute number of ships that would be sunk once a U-boat had penetrated the destroyer screen around the convoy, since there were always more than enough targets and each U-boat had a limited number of torpedoes. So there was safety in numbers simply because one ship was less likely to be picked out from the crowd. Looking at the actual number of ships torpedoed per convoy sailed (including stragglers who failed to keep up with the escorts), the researchers found that it worked out to almost exactly 0.9 ship per convoy regardless of convoy size.
⁶

The mathematician J. H. C. Whitehead shortly afterward produced a paper explaining further why a large convoy did not need as many escorts per ship to afford the same level of protection. Even the 3 + N/10 formula underestimated the benefits of combining small convoys. The chances of a U-boat penetrating the escort screen, Whitehead noted, was basically a function of the linear spacing of the escorts around the convoy’s perimeter. But the length of the perimeter increased very slowly with increasing size of the convoy. It was a familiar geometric principle that occurred frequently in biology: the area within a perimeter increases with the square of the perimeter’s length. To maintain the same linear spacing around the perimeter, the number of destroyers required increased as the square root of the number of ships they were assigned to guard. A 78-ship convoy had a perimeter only one sixth longer than that of a 40-ship convoy; 7 escorts on the larger convoy provided the same level of protection as 6 escorts on the smaller one. Thus by far the most efficient use of the available surface escorts was to employ them in the largest possible convoys practical. Increasing the average size of convoy even by 50 percent, Blackett calculated, would reduce the total number of merchant ship sinkings by half.
⁷

Blackett was well aware what a serious matter he was taking on his shoulders. He and his co-workers “had proved intellectually to themselves that big convoys were safer than small ones,” as Blackett later said, but “before we advised the Navy to make this major change, we had to decide whether we really believed in our own analysis.” Blackett did so for himself by deciding “that if I were to send my children across the Atlantic at the height of the U-boat attacks I would have sent them in a big rather than a small convoy.”
⁸

But at the Anti-U-boat Committee the Admiralty was unimpressed, and dug in its heels. At the February 24 meeting, Lord Leathers, the minister of war transport, urged that the artificial limit of 60 ships be waived as the only way to relieve the increasing backlog of supplies awaiting shipment across the Atlantic. The first sea lord, Admiral of the Fleet Sir Dudley Pound, replied that the “sailing of such large convoys was asking for trouble” and reiterated that 40 ships was the optimal size.

Blackett tried again a week later, pointing out that even if losses increased with larger convoys, total imports would increase as well given that significant numbers of ships were now being delayed by the 60-ship rule:

But, he pointed out, the assumption that losses would increase at all was “unduly pessimistic”; he was just presenting a worst-case possibility, and the evidence was that losses would likely not increase even in absolute numbers. Blackett advanced all of these arguments yet again in an unusually forceful paper produced later that spring (forthrightly titled “The Case for Large Convoys”). In it he also noted that a related advantage of fewer sailings with larger convoys was that the available long-range and VLR aircraft would be able to cover a greater percentage of ships during their perilous passage through the still inadequately protected “air gap.” The calculation was rather complicated, but conferring with the Coastal Command ORS he predicted that air cover would increase 40 percent.

In the end it was the press of import requirements that forced the Admiralty to back down. Blackett’s arguments helped offer some assurance that the change would at least not be a disaster, even if he had failed to convince Pound that it would be a virtue in itself. By late spring and early summer 1943, 80-ship convoys were common. As Blackett had predicted, the large convoys were far more economical in their use of surface escorts. The change allowed a large number of destroyers to be freed up the following year to support the D-Day landings. Blackett later calculated that had he thought to look into the problem in spring 1942 instead of a year later, a million tons of shipping, 20 percent of the total losses, could have been saved in the interim through the adoption of large convoys. But in the rush of other work no one in the Admiralty operational research section had thought of it.

Still, no one on the navy staff had thought of it, either. “The problem forced itself on our notice,” said Blackett, only when the operational researchers began exploring the tangential question Cherwell had raised about the relative effectiveness of escorts. “As in most of the important cases … the really vital problems were found by the operational research groups themselves rather than given them to solve by the Service operational staffs.”
¹⁰

THE U.S. EIGHTH AIR FORCE’S ENTHUSIASM
for bombing the German submarine bases on the Bay of Biscay, which Morse had encountered
during his visit to England in the fall of 1942, was the bastard offspring of mixed motives.

The rapid buildup of the American B-17 and B-24 forces in England since the summer had exposed glaring deficiencies in the organization, training, and abilities of the bomber units. There was no lack of enthusiastic volunteers: the Army Air Forces had so many recruits that by the end of 1942 it had a backlog of 100,000 men awaiting flight training and even enlisted technical positions were so oversubscribed that air force officers estimated they already had all the candidates they needed for the next two years of all-out expansion. In December 1942 voluntary enlistment in the AAF was ended.
¹¹
“The Romance of the Air,” remarked the novelist E. M. Forster in a letter he wrote his friend and fellow writer Christopher Isherwood, “is war’s last beauty parlor.”
¹²

The problem facing the AAF was how to train all of those eager young men fast enough to get them into combat units. Its solution was a kind of assembly-line education that seemed to teach almost nothing. Demoralized instructors, most of them civilian teachers promised rank, promotion, and the chance to put their talents to use serving their country, found themselves wearing private’s stripes and delivering canned lectures they were ordered to follow by rote. One student pilot remembered the eight classes a day he attended as “the saddest, poorest, most incomplete” attempt at education he ever experienced in his life, “the maximum of predigested information in the minimum time.”
¹³

Deployed to England, the crews were ill-prepared and their aircraft plagued with mechanical problems. An inspection report found radio operators who could not send and receive Morse code at the minimum rate of eighteen words per minute, gunners unfamiliar with how to operate their turrets or track a rapidly closing fighter, pilots who had scant experience flying at high altitudes, bombardiers who could not read maps. Most of all, commanders concluded, the men just needed some toughening up, which could only come from actual combat experience of flying through flak and enemy fighters, enduring the freezing cold and low oxygen of high altitude in unheated and unpressurized cabins. From this perspective, bombing the Bay of Biscay ports, which were much closer than targets in Germany, offered an opportunity for the American crews to get their feet wet.
¹⁴

Meanwhile, criticisms in the American press about the slow pace of the Eighth Air Force’s buildup were making the U.S. air force commanders and their political masters in Washington worried. In November 1942,

H. H. “Hap” Arnold, the commanding general of the U.S. Army Air Forces, told General Eaker he was sending from Washington an officer especially qualified for the task of “writing up and presenting to the American public” the success of the heavy bombers to date and explaining their ability to “crush Germany’s capacity to wage war at its source.” A few months later the assistant secretary of war for air, Robert Lovett, nervously called Eaker’s attention to a recent article in
Reader’s Digest
questioning why the American strategic bombers were not yet doing the great things that had been promised of them.
¹⁵
Lovett and Arnold were both eager for some stories that would offer quick proof of the value of U.S. strategic air power to the war effort, and deflect pressures to divert aircraft to other uses or to other theaters such as North Africa, where the airmen would not have the same opportunity to achieve the decisive victory through air power—alone—that they so fervently believed in.

In truth, neither the Eighth Air Force nor the RAF commanders were ever that enthusiastic, deep down, about the operation against the U-boat pens. But they understood politics, too, and thought it might at least divert attention away from the worse prospect of having more of the heavy bombers diverted to antisubmarine patrols. Like Churchill, Roosevelt was also pressing for action in the fall of 1942 to stem the losses of merchant shipping. Eaker confidently assured the president that with 1,000 bombers he could reduce German submarine operations in the Atlantic by 60 percent by destroying the Bay of Biscay bases. Since he had far fewer than that number he was probably hedging his promise to deliver results, while also sensing an opportunity to get more airplanes. In mid-October, with General Dwight D. Eisenhower calling for the defeat of the U-boats as “one of the basic requirements to the winning of the war,” Eaker again pointed to bombing the U-boat bases as the best way to get the job done. “Given enough bombers here we can destroy the submarines where they are built and launched more economically than looking for a needle in a haystack—a submarine in the Atlantic.”
¹⁶

On October 21, Eaker carried out the first raid, sending 90 B-24s and B-17s against L’Orient. Only 15 planes reached the target, the rest turning back because of bad weather. Over the next ten weeks the Eighth Air Force carried out nine more attacks on the U-boat ports, dropping 1,500 tons of bombs and losing 28 aircraft and 300 crewmen killed, wounded, or missing in the process. Analysts examining the attack photographs found that only
6 percent of the bombs dropped by the American aircrews fell in the “target area,” and even that was being generous, since, as they acknowledged, it was based on “a very liberal interpretation of the word ‘Target,’ and it includes all hits and craters which can be seen.”
¹⁷

The AAF’s own scientific experts had pointed out from the start that the concrete roofs of the submarine pens were virtually indestructible and that the related services that supported the port operations were widely spread out in the French towns, so that bombs which missed their target would fall on little of any consequence. “Based upon experimental data, involving tests conducted during the past year in the United States, it is my opinion that none of the U.S. bombs now available to this Command are capable of perforating the roofs of these pens, at least from any practicable bombing height,” the VIII Bomber Command’s operations research section noted on December 8.
¹⁸
A report by the British Ministry of Economic Warfare reached the same conclusion earlier. A memorandum by the British Air Staff in November also noted that the amount of fuel, water, electricity, and general supplies required by the bases was such a small percentage of the total available in each of the port cities that even widespread destruction of the towns themselves would have little effect on U-boat operations from their ports.
¹⁹

Hoping for better results, U.S. air commanders ordered the 31 B-17s assigned to a raid on Saint-Nazaire on November 9 to fly as low as 7,500 feet to improve bombing accuracy. It was practically suicidal. Three planes were shot down and 22 damaged by flak. Once again the photographic interpreters strained to find any evidence that their bombs had done any damage at all. Only 75 of the 344 bombs dropped even showed up on strike and reconnaissance photos of the entire target area; of those, only 8 fell within 600 feet of the port facilities or workshops the planes had been assigned to hit. Saint-Nazaire was hit by five heavy raids in early November; according to agents’ reports the port was back in full operation two weeks later.
²⁰