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Nations at war
White, John F. U Boat Tankers, 1941-45: Submarine Suppliers to Atlantic Wolf Packs. Annapolis, MD: Naval Institute Press, 1998.
Acknowledgments; Preface; Introduction; photos; maps; Epilogue; Bibliography; Index.
Appendices: Results Achieved by the Milk Cows; Spanish Co-operation, 1940-42; Known War Cruises; Principal U boat Types in this Book; U boat Quadrant Map; German Naval Ranks
The German U-boats of World War II continue to fascinate large numbers of readers of military books, and Naval Institute Press proves again to be among the most adept at providing more fascinating reading on the subject.
The latest U-boat book from NIPfollowing in the wake of many recent successes such as their books by Kemp, Niestle, and a pair from Wynnmanages to discover an under-reported aspect of the U-boat campaign and deliver a thorough, interesting exposition. Indeed, White's tale of the undersea tankers grabs and holds the attention as one by one these critical assets hiding in the most remote reaches of the Atlantic are located, attacked, and destroyed. As they are lost, the final shreds of hope for a victorious U-boat campaign are also lost. Besides telling the story of these specialized vessels, the successes and defeats recounted in U Boat Tankers provide a microcosm of the broader U-boat war.
Chapter One outlines the salient facts of the German naval situation at the advent of the Second World War, Kriegsmarine plans, and the initial impetus for designing and deploying U-tankers.
Chapter Two delves into "secret" U-boat refueling operations in Spanish ports and the use of surface supply ships to refuel and reprovision German submarines. In June 1941 nine of these surface supply ships were sunk or captured by the British in the Atlanticthanks to the breaking of German naval codes. White surveys the story of German coding and communication procedures, Enigma, Bletchley Park, Ultra, and British use of their signals intelligence bounty. In fact, the U-boat campaign, the history of the U-tankers, and this book are all as much about signals intelligence as underwater operations. Although Admiral Doenitz feared his codes might have been compromised, a specially convened board of inquiry concluded that communications with U-boats at sea remained secure.
The third chapter continues the saga of code-breaking and sinkings, with surface supply vessels proving to be extremely vulnerable. Despite being in out-of-the-way locations, Atlantis and Python were both surprised while in the process of refueling and sent to the bottom by British cruisers. Despite renewed suspicions, coded Kriegsmarine traffic was still deemed secure.
The entry into the war of the United States, the subsequent campaign against shipping in American waters, and the loss of surface supply ships led to the realization that U-tankers would be required to keep attack boats on station for more than a few days in such distant waters. The ex-Turkish boat UA proved unsuitable for the task, but the first of the purpose-built U-tankers, U-459, arrived off Bermuda on 18 April 1942. Within the next three days the new submarine tanker had refueled and reprovisioned U-108, U-98, and U-333, opening a new era and a new opportunity for Doenitz to press the undersea war against Allied shipping in the most distant reaches of the ocean. U-459 suckled fourteen thirsty boats before returning to France.
Ten of the Type XIV tanker U-boats were constructed and a number of submarine minelayers were also pressed into service as milk cows. White describes in detail the mechanics of rendezvous and refueling on the surface (originally done by trailing behind the tanker, later altered to running alongside), providing fresh bread (the tankers included bakeries) and other food, maintenance and repair, doctor's rounds, ferrying spare parts by rubber dinghy, transferring spare torpedoes, and so on.
Many of the milk cows experienced difficulties with balancing the supplies that they took out with them against the needs of their 'customers'. Most reported that they were overladen with foodstuffs in the early missions and frequently they had to return to base with their supply of four reserve torpedoes untouched. The biggest problem lay with their overall weight during the cruise, affecting trim and diving qualities of the tanker. Many of the cows discovered that they were too light on leaving France and too heavy on their return. The reason was that the light fuel oil was replaced with heavier water as the fuel was pumped out. The designers had assumed that the donation of foodstuffs to other U-boats would compensate for the increase in weight, but in practice few wanted the foods and Steibler (U-461) complained that he practically had to throw the stuff at them in order to get it off his boat. In later patrols, the U-tankers would be heavily ballasted with disposable iron as they left port, and carry fewer comestibles.
White covers the process of escorting U-tankers to and from French ports through the dangerous waters of the Bay of Biscay, procedures for readying the boats for their next patrol, and talks about crew selection and rotation. Pages are devoted to describing day-to-day life aboard the U-tankers with information about alarms and crash dives; these normally took twice as long for the bulky tankers compared to Type VII attack boats, and the difference could mean death.
White also discusses an interesting experiment with underwater refueling; that is, with both boats submerged. This is a technique which might have saved many milk cows, or at least extended their careers, had it been perfected.
The experiment was conducted in anticipation of the day when aircraft reconnaissance would make any other course [of refueling] impossible. Other supplies were transferred the normal way, on the surface; the oil hoses were connected and both boats submerged to a predetermined depth (fifty metres). No submarine can hover underwater; it must sink or rise unless sufficient forward momentum is maintained to enable the hydroplanes to be effective. Both U-boats therefore moved through the water (in line astern, the tanker towing U-445), keeping in touch with their hydrophones, before resurfacing after three hours, refueling complete. Underwater refueling never came to much, owing to the high degree of seamanship required that tended to be lacking in the newly trained crews.
White charts every sailing of the milk cows, recording the dates and routes of their patrols, which boats they refueled and resupplied, quantities of food, fuel, oil, water, parts, and torpedoes transferred. This includes good coverage of operations in the Med and the Black Sea (where cows weren't needed) and the Arctic, the Pacific, and the Indian Ocean (where they were). White notes medical emergencies, replacement sailors dispatched to attack boats, seamen washed overboard, crash dives, convoys spotted, and so on. His material comes from U-boat war diaries and Kriegsmarine records, along with corroborating Allied files.
While all these efforts succeeded in extending the reach of the U-boats, interestingly enough it seems that an unanticipated result of the milk cows permitting such an extension of ranges, time on patrol, and days at sea was a decided contribution to lowering of morale among the hard-worked submariners who consequently spent more time on nerve-wracking missions and less time enjoying the comforts of port.
In May 1942 another milk cowU-116, built as a submarine minelayerrefueled and resupplied a half dozen U-boats in North American waters following U-459's departure. These early fuelings from cows were in large part responsible for the increased number of U-boats operating on the American coast and in the Caribbean, and this in turn led to the remarkable success of more than 200 sinkings. By early June U-459 was back at sea refueling U-boats in the Atlantic. In July she was replaced by her sister ships, U-460 and U-461, on their maiden voyages. U-462 and U-463 followed them into the Atlantic later in the month.
In August 1942 the tanker U-464 was sunk and 53 survivors captured. From their interrogation the Allies learned for the first time of the existence of the milk cows. From that moment, the underwater tankers became a major focus of anti-submarine operations.
In December 1943, after a hiatus of some months, British intelligence resumed cracking U-boat codes and tracking their movements and locations. From this point, much as the surface supply vessels had been swept from the ocean, U-tankers and their customers when ordered by U-boat Command to rendezvous in remote areas began to find Allied air and sea assets already deployed there. The German B-Dienst was also intercepting and decoding RN signals, and in the early months of 1943 it became apparent the Allies knew a great deal about U-boat dispositions. Yet another investigation, however, "proved" German codes remained secure.
The flood of signals from HQ arranging each refueling rendezvous was grist for the Allied signals intelligence mill. Not only were the attack boats at risk, but the cows themselves suffered badly. Despite increasingly heavier anti-aircraft weaponry and standing orders that when under air attack no U-boat could cease firing and dive until its cow was safely away, tanker losses mounted and the ability to freely conduct submarine operations in remote areas declined sharply. Returning boats frantically sought refueling and as they converged on the few remaining tankers they attracted the attention of Allied hunter-killer groups. British intelligence feared that if US escort carrier groups continued to destroy milk cows at such a rate, the Kriegsmarine would realize how completely their communications were compromised.
Eventually the attack boats are forced to suckle each other and it seemed like every patrol became a desperate race as U-boats were vectored to one site after another to find fuel enough to return home. The last purpose-built tanker was sunk in June 1944 and within a few weeks the U-boat bases in France were abandoned as the Allies broke out of the Normandy beachhead, further limiting the extent of U-boat operations.
In breaking the back of the milk cows and attack boats, White makes it clear thatdespite the development of radar, sonar, hedgehog, Fido, sonobuoys, and other technological marvels that helped win the undersea warsignals intelligence, including HF/DF (radio direction-finding), was most critical. Indeed, three of the ten purpose-built cows were located and sunk before they were able to conduct a single refueling. One brief snippet serves to illustrate the highly efficient nature of Allied signals intelligence:
...on 4 June  one these, U-505, was captured by the Guadalcanal carrier group off Dakar. The codebooks were recovered intact, but there was little effect at this stage of the war. Indeed, the US '10th Fleet' discovered that the codebooks and other documents on board U-505 were less up-to-date than their own records, since the U-boat had been at sea for some months.
Paragraphs from White's Preface also make a fitting conclusion:
The published memoirs of the few surviving U-boat commanders who were at sea after mid-1943 make it clear that the men at sea had realised that any broadcast message brought instant retribution, a problem exacerbated by the accuracy of Allied direction-finding equipment used to pinpoint the position of a transmitting U-boat. The older hands would send each other messages couched in terms that would only be understood by the recipient, if they used the radio at all. Yet B.d.U. (U-boat Command) continued to send out radio commands to boats as soon as they had left port instead of providing 'sealed instructions' to be opened at sea. It is true that many U-boats were sunk fortuitouslyfor example, boats caught unawares at night by radar-fitted aircraft while traveling on the surface of the Bay of Biscay, or even in mid-Atlanticbut constant changes to the U-boat ciphers indicated that the Germans had their suspicions.
It must have become apparent that virtually every U-tanker send to refuel boats for remote theatres was quickly sunk after mid-1943, despite selection of the most secluded sea areas for the rendezvous. It seems extraordinary now that U-boat Command did not send out U-boats with written orders to head to a remote part of the ocean, then broadcast repeatedly in cipher from France that a refueling was to take place at this remote area, and order the U-boat to report back what happened. Several U-boats ordered to rendezvous with a milk cow in mid-Atlantic did report to base that they found only destroyers at the rendezvous, and the cow was never seen again.
Doubtless part of the problem lay with wishful thinking, for any interference with radio commands negated the whole basis for wolf-pack tactics, by which many boats were directed to a convoy located by one of their number. It is to be hoped that our current naval planners have not put the same unquestioning faith in their machine-operated ciphers as did the German Navy, particularly with the much publicised advances in computer decryption techniques.
A very interesting book. White's prose is not the most polished, but sufficiently energetic to carry the day. Well worth reading.
Available from online booksellers, local bookshops, or directly from NIP.
Thanks to Naval Institute Press for providing this review copy.
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Reviewed 23 October 1998
Copyright © 1998 by Bill Stone
May not be reproduced in any form without written permission of Stone & Stone