Dönitz intensifies the U-boat war

On 24 September 1939 German submarines in the Atlantic received new orders that relaxed the restrictions imposed on them by prize law since the outbreak of war. Merchant ships that, having been stopped by a U-boat, tried to call for help by radio were henceforth to be seized or sunk. French ships were no longer to be spared and were to be treated in the same way as British ones. U-boats were also permitted to lay mines off the French coast. The changes had been pressed for by the commander of the U-boat arm, Commodore Karl Dönitz; the decision was taken by the Naval War Staff (Seekriegsleitung) in the naval high command, with the approval of Adolf Hitler. It was the first in a series of steps that within a few months led Germany to unrestricted submarine warfare.

Some accounts state that on this day Dönitz “considerably relaxed” the prize rules, ordering ships transmitting radio signals to be sunk without warning, permitting attacks on smaller Allied passenger ships and opening the war against French shipping. The surviving war diary of the U-boat command allows this to be stated more precisely. The decision of 24 September did not concern passenger ships: the existing ban on attacking them remained in force. Passenger ships were redefined only on 2 October, and attacks on ships sailing without lights were likewise permitted, within a limited area, only at the beginning of October. Nor were ships using their radio to be sunk without warning; they were to be sunk after being stopped, if they transmitted signals nonetheless.

War by the rulebook

The German navy entered the war with instructions to wage war on merchant shipping in accordance with the prize regulations. In 1936 Germany had acceded to the London Submarine Protocol, which restated the rules of the London Naval Treaty of 1930. A submarine could stop a merchant ship and check whether it was carrying contraband, but it could sink it only after ensuring the safety of the crew and passengers. Warships, troop transports, ships sailing in convoy under warship escort and ships offering resistance could be attacked without warning.

After the sinking of the Athenia on 3 September, Hitler, who was counting on a swift settlement with Britain and France once Poland had been defeated, additionally ordered that passenger ships were not to be attacked, even in convoy. France was spared in particular. On 3 September the naval high command forbade any action against French merchant ships other than in self-defence, and on 6 September it added that ships identified as French were not even to be stopped. Dönitz noted with irritation at the time that French ships were being treated better than neutral ones. Hitler wanted France to be the first to open fire, and he hoped that after Poland’s defeat the government in Paris would agree to peace.

The experience of the first weeks

Waging war according to prize rules was proving increasingly dangerous for the submarines. A surfaced U-boat that stopped a ship with a warning shot, then waited while the papers were checked and the crew abandoned ship, was defenceless against aircraft and escort vessels. From the first days of the war the British armed their merchant ships with guns and instructed masters to report by radio every submarine they encountered. In this way merchant ships became part of the British surveillance system. Many of them, when stopped by a U-boat, immediately sent out a distress call giving their position. Within a few dozen minutes aircraft would appear over the spot.

Commanders returning from patrol reported such cases to Dönitz. On 23 September he wrote in his diary that ships which used their radio after being ordered to stop were thereby “supporting the enemy’s anti-submarine warfare”, and he asked the high command for a decision. He also pointed out that the question of French ships was becoming ever more pressing, since convoys carrying British troops to France crossed the English Channel by night, and at night it was impossible to tell a French ship from a British one. Two days earlier, on 21 September, the Seekriegsleitung had ordered that attacks on French ships were to be avoided at all costs, which in practice ruled out operations in the Channel. Dönitz protested, and the order was withdrawn the same day, restoring the previous position: convoys north of the latitude of Brest could be attacked even when escorted by French warships.

The decision of 24 September

On 23 September at Sopot, where Hitler was staying during the September Campaign, the Commander-in-Chief of the Kriegsmarine, Grand Admiral Erich Raeder, briefed Hitler, in the presence of the chief of the OKW, Wilhelm Keitel, on the situation at sea and presented proposals for intensifying the war on shipping. According to German naval records, Hitler agreed to a gradual intensification of the war on trade, and two days later he released for operations the two “pocket battleships” that had been waiting in hiding in the Atlantic since August.

On 24 September the Seekriegsleitung sent Dönitz a secret ruling. It read as follows: French ships were to be treated in the same way as English ones; as regards passenger ships, the existing orders remained in force; merchant ships that used their radio after being stopped were to be taken into port or sunk; mines could be laid off the French coast. That same day the boats at sea received the corresponding order by radio.

The change was greater than it might seem. A ship that sent out a signal after being stopped by a U-boat was in any case regarded by the Germans as offering resistance. But the new orders gave commanders general licence to sink such ships, and according to the commanders’ reports, which Dönitz recorded in his diary, ships transmitted signals “in a very great many cases”. The lifting of protection from French ships meant, moreover, that for Germany too the war with France had ceased to be a make-believe war.

Further steps

The orders of 24 September opened the way to further ones. According to the findings of the International Military Tribunal at Nuremberg, an order had been issued as early as 21 September to attack all ships sailing at night without lights in the English Channel. Dönitz’s diary shows, however, that on that day the matter was still in dispute, and that the Seekriegsleitung designated the first area around England in which darkened ships could be sunk without warning on 2 October. On the same day it was decided that only ships able to carry more than 120 passengers were to be regarded as passenger ships, which still could not be attacked. Smaller vessels that also carried passengers thereby lost their protection. On 1 October Dönitz was promoted to rear admiral. On the same day the British Admiralty announced that masters of merchant ships were to ram submarines whenever possible.

On 4 October the area in which darkened ships could be attacked was extended westwards to 15 degrees west, and U-boats were given the right to attack armed merchant ships without warning. On 17 October, after Hitler’s peace offer had been rejected by London and Paris, an order was issued to attack all enemy merchant ships without warning. A few days later the area of operations against darkened ships was pushed out to 30 degrees west, and at the end of October attacks on passenger ships sailing in enemy convoys were permitted. From January 1940 U-boats could also sink neutral ships without warning in designated zones around the British Isles. Six months after 24 September little remained of the former restrictions.

Significance

The orders of 24 September were the first step along a road that Germany had already travelled in the First World War: from war according to prize rules to unrestricted submarine warfare. In 1917 such a decision had drawn the United States into the war. In 1939 Berlin went down this road more cautiously, step by step, mindful of the reaction of the neutral states, and especially of America, which had just declared its neutrality. Each escalation was justified by British actions: the arming of merchant ships, radio reports and the orders to ram.

The Germans were not alone in this. From the spring of 1940 the British too declared zones in the waters off Germany and Norway in which their submarines attacked without warning, and on the very first day of the war in the Pacific, in December 1941, the United States ordered unrestricted submarine warfare against Japan. This circumstance played an important part after the war. At his trial before the International Military Tribunal at Nuremberg, Dönitz argued in his defence that until October 1939 his boats had observed the law, and that thereafter they had been responding to the British arming of merchant ships. In its judgment of 1 October 1946 the Tribunal held that, in the circumstances of the case, it could not convict him for the conduct of the war against armed British merchant ships. It did, however, find that the sinking of neutral ships without warning in declared operational zones, and Dönitz’s order not to rescue survivors, violated the London Protocol. Yet in view of similar Allied practices, confirmed by the American Admiral Chester Nimitz, Dönitz’s sentence was not based on breaches of the law of submarine warfare. He was sentenced to ten years’ imprisonment for taking part in waging aggressive war and for war crimes.