The German blockade of the British Isles

On the evening of 17 August 1940 Berlin announced a “total and unconditional blockade of England”. That day the Reich government handed the governments of the neutral states a note declaring the entire sea area around the British Isles an operational zone. Any ship entering it “exposes itself to destruction not only by mines but also by other means of warfare”, and the German government therefore “once again urgently warns against entering this endangered area”. In practice this meant that German submarines, surface warships and aircraft could attack any ship in those waters without warning, whatever its flag. The zone coincided almost exactly with the combat area that President Franklin Delano Roosevelt had closed to American ships in November 1939: it covered the waters around Britain and Ireland, from the Bay of Biscay to the North Sea, and reached far out into the Atlantic.

It is usually written that the blockade was declared by Adolf Hitler. The decision was indeed his, but formally the declaration was made by the Reich government, and the executive orders for the navy and the air force were issued by the Wehrmacht High Command (OKW). Three days later, on 20 August, Italy sent a similar note to the neutral states, declaring an operational zone in the waters along the British coasts in the Mediterranean, the Red Sea and Africa.

From secret zones to an open declaration

Against British and French ships the German U-boats had been waging war without warning since October 1939. Towards neutral ships the navy acted more cautiously. In the winter of 1939–1940 Hitler agreed to the designation of zones in which they could be sunk without warning, but these zones were secret and lay close to the British coasts, and the sinkings were meant to look as though the ships had struck mines. Admiral Karl Dönitz’s defence counsel at Nuremberg, Otto Kranzbühler, later estimated that by 17 August 1940 such attacks had been permitted in an area of about 200,000 square miles. The main reason for the caution lay across the ocean: Berlin did not want to hand Roosevelt arguments against the American isolationists, and it remembered that in 1917 the declaration of unrestricted submarine warfare had drawn the United States into the war. Since the autumn of 1939 Grand Admiral Erich Raeder had been asking for a formal declaration of a “siege of England”, but the decision had been put off each time.

The summer of 1940 brought that moment. After the defeat of France the Germans had ports on the Bay of Biscay and in Norway. From July U-boats were putting into Lorient, which shortened their passage to the Atlantic by hundreds of miles. Italy had entered the war, and its submarines were just beginning to move to their new base at Bordeaux. Britain had rejected the peace offer that Hitler made in the Reichstag on 19 July. On 1 August, in Directive No. 17, he ordered the air and sea war against England to be intensified, and on 13 August the Luftwaffe began its massed attacks on RAF airfields. The declaration of the blockade was meant to be the naval counterpart of this offensive: to show the world that it was England, not Germany, that was now under siege.

The note of 17 August

The text of the note, issued by the German news agency and reprinted the next day in the Axis press, was for the most part an indictment. Britain, it claimed, had been violating the law of the sea since the start of the war: it had declared food contraband in order to starve the population of the Reich, extended its blockade to all German exports, armed merchant ships against submarines, and abused neutral flags. The note reproached the British for seizing Norwegian, Danish, Dutch, Belgian and French ships, whose crews had been “forced into the service of England”; for detaining in British ports ships of countries as remote from the war as Japan, the USSR and Sweden; and for the navicert system – British certificates without which a neutral ship could not safely carry its cargo. To this it added the latest grievance, from July: the British announcement that German rescue aircraft, Heinkel He 59 seaplanes bearing red crosses, would be shot down.

Germany, the note declared, had responded by sinking five million tons of merchant shipping and damaging a further million and a half. This was a propaganda figure. According to post-war British tallies, between September 1939 and the end of July 1940 the Allies and the neutrals lost ships totalling some 2.7 million gross registered tons from all causes, from torpedoes, mines, bombs and raiders. The note ended by turning round the words Winston Churchill had spoken in the autumn of 1939 about the besieged German fortress: the besieged fortress, according to Berlin, was now England. To the “failed hunger blockade against German women and children” the Reich opposed the “total blockade of the British Isles”, and England, which had “rejected the Führer’s last appeal for peace”, would henceforth be treated “with the same lack of scruple”.

Blockade or operational zone

The word “blockade” was more a political slogan than a legal term. Under the Declaration of Paris of 1856 a blockade is binding only if it is effective – that is, if the blockading power’s forces actually close off access to the enemy’s ports. The Kriegsmarine could not station warships off Liverpool or Glasgow. What was proclaimed on 17 August was in essence an operational zone in which the Germans reserved the right to sink any ship. Both sides had already used such zones in the First World War, and the Germans later pointed out that from 8 May 1940 the British too had been sinking all ships without warning in the Skagerrak.

The boundaries of the zone were carefully chosen. Since they coincided with the area forbidden to Americans by the Neutrality Act, American ships had no business there and ran no risk of meeting a U-boat. All the other neutral flags still trading with Britain, on the other hand, could fall victim: Swedish, Greek, Finnish, Hungarian, Spanish, Portuguese or Irish. According to Kranzbühler the zone covered some 600,000 square miles of sea; the prosecutors at Nuremberg, counting the land area of the British Isles and western France as well, spoke of 750,000.

The zone in practice

In the Atlantic the declaration changed little in the day-to-day work of the U-boats. In the second half of August a dozen or so boats from Lorient, Bergen and German ports were operating off the North Channel, through which convoys entered and left the ports on the Clyde and the Mersey. They mostly attacked ships sailing alone or straggling behind convoys, and increasingly the convoys themselves, which were then escorted by one or two warships, since British destroyers were waiting in port for a German landing. According to figures compiled by uboat.net, in August 1940 submarines sank 57 ships totalling more than 287,000 gross registered tons and damaged nine. A period began that U-boat crews called the “happy time”. Commanders such as Otto Kretschmer, Joachim Schepke and Engelbert Endrass sank several ships in a single patrol. On 25 August, over the Atlantic, the first ship – the British steamer Goathland – was sunk by a long-range Focke-Wulf Fw 200 Condor, an aircraft that was to become the scourge of the convoys.

Neutral ships were soon sinking after the blockade was declared. On 19 August the submarine UA stopped the Hungarian steamer Kelet, sailing in ballast from Wales to America, with gunfire and then finished her off with a torpedo and shells. The ship had on board survivors of the British Clan Macphee, sunk three days earlier, and six of them were killed. The next day Endrass’s U-46 torpedoed the Greek ship Leonidas M. Valmas, carrying timber from Canada to Dublin; sixteen people died. On 27 August the Greek Theodoros T. went down, and on 28 August U-101 sank the Finnish steamer Elle in convoy SC 1. Greece, whose cruiser Elli had been sunk off Tinos on 15 August, was still a neutral country. The most notorious attack came at midnight on 30–31 August: U-60 torpedoed the Dutch liner Volendam in convoy OB 205; she was carrying 320 British children evacuated across the ocean to escape the air raids. The ship stayed afloat, the children were rescued by other ships of the convoy, and the only casualty was a seaman who fell overboard.

London’s answer came on 20 August in the House of Commons. Churchill dismissed the German declaration briefly. Noting that Hitler had also declared a strict blockade of the British Isles, he remarked: “No one can complain of that. I remember the Kaiser doing it in the last war.” At the same time he announced that Britain would maintain a strict blockade not only of Germany but also of Italy, France and all the countries occupied by Germany, and refused to let through food for the occupied nations, as the former President of the United States Herbert Hoover, among others, had urged. Responsibility for hunger in Europe, in his view, lay with those who had plundered it.

The Italian note of 20 August

According to a widespread version, on 20 August Italy declared a blockade of British ports in the Mediterranean. That was how the press of the time presented it, but the note itself, like the German one, was a declaration of an operational zone. In it Benito Mussolini’s government reminded the neutral governments of its warning of 15 June, issued a few days after Italy entered the war: ships bound for enemy ports sailed at their own risk once they came within 30 miles of the enemy’s coast. Now Rome went further. A belt of sea along the coasts of British colonies, protectorates and mandated territories, and of countries such as Egypt in which British land, naval and air forces were stationed, became, according to the note, a “permanent zone of operations”. This applied in particular to the British coasts in the Mediterranean, the Red Sea and the Gulf of Aden, the British colonial coasts in Africa, and the coasts of Egypt and the Sudan. Any ship entering them “exposes itself to destruction by mines and other means of war”, and the Italian government disclaimed all responsibility. It stipulated only that it did not intend to hinder the passage of neutral ships through straits that were a necessary route for shipping.

Far less force stood behind this declaration than behind the German one. In the Mediterranean the Royal Navy had the upper hand: in July it had clashed with the Italian fleet off Calabria, and on 17 August its battleships bombarded Italian positions at Bardia and Fort Capuzzo. In the second half of August Italian submarines prowled off Gibraltar, near Crete, in the Aegean and off the coasts of Palestine and Cyprus, and Italian aircraft bombed Malta, Alexandria and Haifa, but there were few neutral ships in those waters. The note of 20 August mattered above all politically: Italy was joining the German “blockade” and announcing that the war at sea now embraced the whole British Empire from Gibraltar to Aden.

Significance

The total blockade remained the basis of Germany’s war on shipping until the end of the war. In the spring of 1941 the Germans extended the zone as far as Iceland and the waters of Greenland, ever closer to waters already patrolled by the US Navy; in the autumn of 1941 the first clashes between American destroyers and U-boats took place in the North Atlantic. In the autumn of 1940 Dönitz began sending his boats against convoys in groups – “wolf packs” – and in October inflicted the first severe defeats on convoys sailing from Canada. In the whole of 1940 the Allies and the neutrals lost ships at sea totalling nearly four million gross registered tons. Britain, however, was not starved: the convoys kept sailing, and in September 1940 the United States handed over fifty old destroyers in exchange for bases.

After the war the operational zones came before the International Military Tribunal at Nuremberg. The Tribunal found that Dönitz’s order to sink neutral ships without warning in these zones violated the London Protocol of 1936 on submarine warfare, which made no exception for zones. It noted, however, that in view of the British order concerning the Skagerrak of 8 May 1940, and of Admiral Chester Nimitz’s statement that the Americans had waged unrestricted submarine warfare in the Pacific from the first day of the war with Japan, Dönitz’s sentence was not assessed on the ground of his breaches of the law of submarine warfare. The blockade proclaimed on 17 August 1940 was thus on the one hand merely a continuation of a practice both sides were already following, and on the other an open admission that in the seas around England neutrality no longer protected anyone.