Kriegmarine Command Doctrine

German Kenngruppenheft (a U-boat codebook with grouped key codes)

The strategic and operational impact of Allied codebreaking also played a critical role in ensuring Allied victory in the Atlantic. The history of efforts to break the German codes during the Second World War—“the Ultra secret”—is well known. The Kriegsmarine’s codes were among the last to be routinely read, but by 1941 British codebreakers were beginning to penetrate the German navy’s main code. Although the definitive impact of codebreaking is impossible to establish, Hinsley, the author of the official and most authoritative account of Ultra and its significance, wrote of the battle of the Atlantic: “The very fact that the struggle was so prolonged and so finely balanced suggests that the ability to read [German] communications must have been an asset of crucial importance to the Allies.” Codebreaking allowed the Allies to reroute shipping, reinforce threatened convoys, disrupt U-boat patrols, sink important German assets such as the U-tankers needed to replenish the fuel and supplies of the U-boats at sea, and gain remarkable insight into the workings of the U-boat command structure.

In retrospect it is clear that, at the tactical, operational, and strategic levels of warfare, the Germans’ reliance on radio proved their undoing in the Atlantic. A highly centralized command structure failed, not because it denied subordinate commanders latitude in their operations, but because the network of communications itself, thanks to insecure codes, was open to the enemy.

Would the German navy have fared better with a less centralized system of command and control, perhaps akin to that employed by the Americans in their submarine campaign in the Pacific? Had BdU used such a system, deploying individual U-boats to hunt singly while maintaining radio silence, the operations of the submarine force would undoubtedly have suffered a substantial loss of efficiency. But at the same time, had their radio silence deprived the British of the wealth of intelligence they gleaned from the transmission of data demanded by BdU— names of U-boat commanders, location of boats, fuel capacity, number of torpedoes, course, speed, current orders, Dönitz’s plans and intentions and even state of mind—the effectiveness of Allied operations would have suffered as well. As for the net loss or gain, no definitive answer can be given.

It should be noted that not everyone within the Kriegsmarine high command, or even the U-boat arm, supported Dönitz’s plans for group attacks. One prewar naval staff study presciently argued “that the wireless traffic necessary would forfeit surprise and aid detection of the boats by the enemy.” Dönitz’s eve-of-war maneuvers in the Atlantic revealed many shortcomings of his concept of operations, and fed the doubts of those who opposed him. Moreover, after the war began, the Germans achieved some of their greatest successes early on, when their naval codes were not yet compromised and before they began operating in groups or wolfpacks. Before late 1941 most U-boats hunted alone, as they had in the Great War, and as American submarines did in the Pacific. Not until the first quarter of 1943 were the majority of the Allied ships sunk by U-boats vessels that had been sailing in convoy. In the first twenty-eight months of war, nine hundred Allied convoys crossed the Atlantic, but Dönitz’s U-boats achieved major victories, that is, sinking six or more confirmed ships, on only nineteen occasions. According to the historian Clay Blair, “although occasionally successful, group or ‘wolf pack’ tactics were on the whole a failure.” While it is impossible to prove, Dönitz’s heavily centralized system of command and control may well have decreased the fighting power of his submarine force.