Tag Archives: code-breaking

U-boats, the Zimmermann Telegram and the US Entry into the War

On 22 December 1916 Admiral Henning von Holtzendorff, the Chief of the Admiralty Staff of the Imperial German Navy, sent Field Marshal Paul von Hindenburg, the Chief of the General Staff, the last of a series of memos advocating that Germany adopt unrestricted submarine warfare.[1] Unrestricted submarine warfare meant sinking merchant ships without warning. German U-boats were then surfacing in order to check the nationality of merchant ships before opening fire. This was done largely to avoid the problems that would ensue if US citizens were killed.[2]

Holtzendorff argued that Germany had to win the war by autumn 1917 or else it would finish with the exhaustion of all the belligerents, which would mean disaster for Germany. The Italian and French economies had been so weakened by the war that they were able to continue to fight only with British support. The Germans had to break the British economy in order to win the war, and the way to do this was to attack the British merchant fleet. Extra demands were being placed on it because Britain imported much of its food and the 1916 global grain harvest had been poor. This meant that Britain would have to replace imports from Canada and the USA with grain from Argentina, India and especially Australia.[3]

Holtzendorff thought that a destruction of 600,000 tons of merchant shipping per month would reduce British trade ‘by 39% within five months. This would not be bearable’.[4] He admitted that he could not ‘guarantee that a campaign of unrestricted submarine warfare’ would force a British surrender within five months.[5] However, acting in accordance with cruiser rules would mean sinking only 400,000 tons per month, reducing British trade by only 18%, which was not enough. Holtzendorff claimed that this was the actual rate achieved over the two previous weeks.[6] The actual losses, shown in the table below, were a little lower.

The British, however, were concerned even at the level of losses of late 1916. In October, Admiral Sir John Jellicoe, who replaced Admiral Sir Henry Jackson as First Sea Lord, the professional head of the Royal Navy, in late November, warned the Admiralty that the losses of British and neutral merchant ships might by the summer of 1917 reduce imports of food and other necessities to a level that would force the Allies to accept worse peace terms than were justified by the European military situation. Admiral Sir David Beatty, who succeeded Jellicoe as C.-in-C. of the Grand Fleet, said that the danger was ‘jeopardising the fate of the nation and seriously interfering with the successful prosecution of the war.’[7]

Holtzendorff  wanted to avoid war with the USA if possible but argued that the risk of it happening should not stop Germany ‘from making use at the decisive moment of a weapon that promises victory.’[8] He thought that the USA would not be able to replace the lost merchant shipping and that there would be insufficient transports to take US troops to Europe. He expected that the USA would make peace when Britain as it would not be able to do as much damage to Germany as U-boats did to its commerce and would want an early return to economic prosperity.[9]

The decision to launch unrestricted submarine warfare from 1 February 1917 was made at a meeting held on 9 January. Chancellor Theobald von Bethman-Hollweg, who had until then opposed unrestricted submarine warfare, finally agreed to it, commenting it that it was ‘the last card.’[10]

On 1 February 1917 the Germans had 105 U-boats available, with new construction taking their strength to 129 by 1 June. They had at least 120 for the remainder of 1917 and 124 at the end of the year. [11]

The U-boat campaign was a military success, as shown by the following table:

British tonnage sunk (excludes fishing vessels) World tonnage sunk (includes British and foreign fishing vessels
October 1916 176,248 353,660
November 1916 168,809 311,508
December 1916 182,292 355,139
January  1917 153,666 368,521
February 1917 313,486 540,006
March 1917 353,478 593,841
April 1917 545,282 881,027

Source: C. E. Fayle, Seaborne Trade, 3 vols (London: HMSO, 1920), vol. iii, p. 465.

However, it resulted in US President Woodrow Wilson breaking off diplomatic relations with Germany on 3 February.[12] He, Congress and the US public were not yet ready to enter the war.

On 16 January Arthur Zimmermann, the German Foreign Minister, sent a telegram to Count Bernstorff, the German ambassador in Washington that he was to forward to Heinrich von Eckhardt, the German minister in Mexico City. Von Eckhardt was to offer the Mexican government an alliance if war broke out between Germany and the USA. The Germans would provide financial aid to Mexico, which would regain the territory that it had lost to the USA in the Mexican-American War of 1846-48 after a victorious war. The Mexicans were also to attempt to persuade Japan to change sides.[13]

The British had destroyed the German cable communications with the rest of the world early in the war. The Germans, however, had access to two neutral cables to the USA: a Swedish one that they had been allowed to use since early in the war; and a US one that Wilson had allowed them to use when he was attempting to mediate between them and the Allies. Both passed through Britain, which could therefore intercept them. The simplicity of American codes and cyphers enabled the British code breakers of Room 40 to break them. They also had a copy of the German diplomatic code book that was captured when Wilhelm Wassmuss, a German agent in Persia, was forced to flee without his baggage.[14] The British and Russians had captured German naval code books in 1914.

On the morning of 17 January Captain Reginald ‘Blinker’ Hall, the Director of Naval Intelligence, was handed a partial translation of the intercepted cable.[15] The code was in a variant of the one captured from Wassmuss and the parts that could not be decoded included details of the terms offered by Germany to Mexico. Showing it to the Americans risked revealing to them that the British were intercepting neutral diplomatic traffic and to the Germans that their diplomatic codes had been broken. Hall, perhaps hoping that the USA might enter the war anyway, sat on the telegram until 5 February, when he showed it to the Foreign Office.

By 10 February British agents had obtained a copy of it from the Mexico City telegraph office. The German legation there used a simpler code than the one used between Berlin and Washington, and the British were able to fully decode it. It could now be passed to the Americans without them realising that the British were intercepting Swedish and US diplomatic cables. The telegram, available online at the Great War Primary Document Archive, read:

Berlin, January 19, 1917

On the first of February we intend to begin submarine warfare unrestricted. In spite of this, it is our intention to endeavor to keep neutral the United States of America.

If this attempt is not successful, we propose an alliance on the following basis with Mexico: That we shall make war together and together make peace. We shall give general financial support, and it is understood that Mexico is to reconquer the lost territory in New Mexico, Texas, and Arizona. The details are left to you for settlement….

You are instructed to inform the President of Mexico of the above in the greatest confidence as soon as it is certain that there will be an outbreak of war with the United States and suggest that the President of Mexico, on his own initiative, should communicate with Japan suggesting adherence at once to this plan; at the same time, offer to mediate between Germany and Japan.

Please call to the attention of the President of Mexico that the employment of ruthless submarine warfare now promises to compel England to make peace in a few months.

(Secretary of State)

Arthur Balfour, the British Foreign Secretary, handed it to Walter Page, the US ambassador to London on 23 February. It was published in the USA on 1 March. A minority of Americans argued that it was a forgery. Hall took steps to prove to that it was genuine, but these proved unnecessary when Zimmermann admitted on 3 March that he had sent it.[16]

Wilson had already decided to ask Congress for permission to arm US merchant ships, which would have almost certainly have resulted in an incident that led to war. The measure was passed overwhelmingly by the House of Representatives but was filibustered out of the Senate. Wilson decided to go ahead anyway. On 20 March, after a number of US merchant ships were sunk by U-boats, he obtained the unanimous consent of his cabinet for a declaration of war. [17] On 2 April the House of Representatives voted 373 to 50 in favour of war, with the formal declaration coming on 6 April.[18]

The Germans thought that they would have starved Britain into surrender before the USA, which in April 1917 had an army of 213,557 men and 55 aircraft, 51 of them obsolete, could make a decisive difference. However, by the end of the war 1.97 million US troops had been sent to the Western Front, with no troopships being sunk on the way from the USA to Europe. By the summer of 1918 the USA was sending 536,000 tons of supplies per month to France, with a troop or cargo ship leaving every five hours. The USN committed 68 destroyers and 121 submarine chasers to the battle against the U-boats.[19]

This link, to a new exhibit at Arlington National Cemetery marking the 100th anniversary of American involvement in World War I, was kindly pointed out to me by G.P. Cox, writer of the excellent Pacific Paratrooper blog.


[1] D. Steffen, ‘The Holtzendorff Memorandum of 22 December 1916 and Germany’s Declaration of Unrestricted U-Boat Warfare’, Journal of Military History 68, no. 1 (2004), pp. 215-16.

[2] A. J. Marder, From the Dreadnought to Scapa Flow; the Royal Navy in the Fisher Era, 1904-1919, 5 vols (London: Oxford University Press, 1961-70). vol. iv, p. 51.

[3] Steffen, ‘Holtzendorff’, pp. 219-20.

[4] Ibid., p. 221. This and subsequent quotations are from Holtzendorff’s memo, which is reproduced in Steffen’s paper.

[5] Ibid., pp. 220-21.

[6] Ibid., p. 222.

[7] J. S. Corbett, H. Newbolt, Naval Operations, 5 vols (London: HMSO, 1938). vol. iv, pp. 324-25.

[8] Steffen, ‘Holtzendorff’, p. 222.

[9] Ibid.

[10] Marder, From. vol. iv, p. 51.

[11] P. G. Halpern, A Naval History of World War I (London: UCL Press, 1994), pp. 338-39.

[12] Ibid., p. 340.

[13] D. Stevenson, 1914-1918: The History of the First World War (London: Allen Lane, 2004), p. 313.

[14] C. M. Andrew, Secret Service: The Making of the British Intelligence Community (London: Heinemann, 1985), pp. 107-8.

[15] Hall was promoted Rear Admiral on 27 April 1917. His nickname resulted from a chronic facial twitch.

[16] Andrew, Secret, pp. 110-13.

[17] Stevenson, 1914-1918, p. 317.

[18] H. H. Herwig, The First World War : Germany and Austria-Hungary, 1914-1918 (London: Arnold, 1997), p. 320.

[19] Ibid.


Filed under Political History, War History

Allied Capture of German Naval Code Books

In the early hours of 26 August, the German light cruiser SMS Magdeburg ran aground at Odensholm lighthouse off Estonia whilst participating in a sweep against Russian patrols in the Gulf of Finland. The destroyer SMS V26 had to abandon her attempts to free Magdeburg when the Russian armoured cruiser Pallada and the protected cruiser Bogatyr appeared.

The Germans tried to scuttle Magdeburg, but were only partially successful. One of her four copies of the Signalbuch der Kasierlichen Marine (SKM), the German navy codebook, was burnt and two thrown overboard. However, the Russians recovered the latter two from the sea and the fourth from the captain’s safe. They later scrapped Magdeburg where she lay.

The Russians retained two of the codebooks for themselves and offered the third to the British, provided that a British ship collected it. This did not happen immediately, but the Admiralty received the codebook on 13 October.

Winston Churchill, then First Lord of the Admiralty, later wrote that Britain ‘received from our loyal allies these sea-stained priceless documents.’[1] Christopher Andrew and Robert Massie both note that the copy of the SKM in the UK National Archives [ref ADM 137/4156] is not sea-stained.[2] The Russians kept the two copies retrieved from the sea and gave the British the one from the captain’s safe.

As well as the SKM codebook, the British obtained a set of the German squared charts of the North Sea and Heligoland Bight that used to identify the location of German and enemy forces. Arthur Marder writes that Churchill and The Naval Staff of the Admiralty, a Naval Staff Monograph, both state that they were provided by the Russians. However, he goes on to say that Lieutenant W. F. Clarke RNVR, who worked in codebreaking, says in an unpublished paper called ‘Jutland’ that they were from the safe fished up by the trawler.[3]

It took some time until the British could read German naval signals sent using the SKM. Weather reports were encoded only by it, but other ones were re-ciphered. By early November, Fleet Paymaster Charles Rotter, a Naval Intelligence Department German expert, had realised that the re-ciphering was a simple substitution table. The key was changed periodically, but later ones were broken more quickly.

The SKM was the second German naval codebook obtained by the British. The SS Hobart, a German merchant ship, had been boarded by Australians off Melbourne on 11 August. They seized a copy of the Handelsverkehrsbuch (HV), which was used principally for communications between warships and merchantmen, but was also used by naval shore bases and later by U-boats and Zeppelins.

The Australians did not initially realise the importance of their prize and it then took time to send it to Britain, so the Admiralty did not receive it until late October.

The British obtained the third German naval codebook, the Verkehrsbuch (VB), when a trawler caught a lead-lined chest on 30 November. It had been thrown overboard by a German destroyer sunk on 17 October. The VB was used for cable communications with naval attachés and warships abroad and by admirals at sea.

The ability to read German codes would become very significant later in the war, but it took time for the Admiralty to get its decryption operation, known as Room 40 after its original office, working well. At first, the civilian cryptographers did not always understand naval matters and some naval staff officers looked down on them. The Admiralty was also excessively secretive with the decrypts, meaning that it did not always make the best use of the intelligence. Paul Halpern comments that ‘Room 40 would not reach its peak of efficiency and become a true intelligence centre until much later in the war.[4]


[1] W. S. Churchill, The World Crisis, 1911-1918, 5 vols (London: Odhams Press, 1939), v, Kindle edition, location 7846 out of 9432.

[2] C. M. Andrew, Secret Service: The Making of the British Intelligence Community (London: Heinemann, 1985), p. 89; R. K. Massie, Castles of Steel: Britain, Germany, and the Winning of the Great War at Sea (London: Jonathan Cape, 2004), footnote, p. 316.

[3] A. J. Marder, From the Dreadnought to Scapa Flow; the Royal Navy in the Fisher Era, 1904-1919, 5 vols (London: Oxford University Press, 1961-70), ii, footnote 2, p. 132. Marder says that Captain Stephen Roskill, whosse papers are now at Churchill College, Cambridge, had a copy of Clarke’s paper.

[4] P. G. Halpern, A Naval History of World War I (London: UCL Press, 1994), p. 37.


Filed under War History

The Eagle Unbowed: Poland and the Poles in World War II – Halik Kochanski

On 23 January 2013 I attended a talk given by Dr Halik Kochanski at the National Army Museum in London on her book The Eagle Unbowed: Poland and the Poles in the Second World War. It was part of a regular series of talks that are held at the NAM on Thursday lunchtimes.

She argued that this is the first book published since the fall of Communism to cover the full story of Poland in World War II. Previous works have concentrated on Poles in the Battles of Britain and Monte Cassino, the Holocaust and the Warsaw Uprising.

Poland had a population of 32 million in 1939, which was made up of 22 million Poles, 4.5 million Ukrainians, 3 million Jews, 1 million Belarusians, 0.75 million Germans and 0.75 million people described as ‘locals.’ A total of 6 million of them were killed in the war, only 10% in military actions. The dead included 90% of the Jews. Five million of the pre-war population were outside the altered post-war borders of Poland at the end of the war.

Poland was in a hopeless position in 1939, with only 1 million troops to defend itself against a German attack from three sides. The Polish plan was to defend and withdraw slowly, launching a counter-attack once the Western Allies had drawn off the Germans.

This plan failed because of the speed of the German Blitzkrieg and because the British and French did little: they were preparing for a long war.

It is a myth that the Polish cavalry charged tanks. There was an action where Polish cavalry successfully charged German infantry but were then surprised by German armour.

It is also untrue that the Polish Air Force was destroyed on the first day. It managed to disperse and continued to fight.

The Poles had few tanks, but the 10th Cavalry (Mechanised) Brigade, the only Polish armoured unit, put up a good fight. Its commander, General Stanislaw Maczek, later commanded the Polish 1st Armoured Division, which fought in Normandy in 1944 and captured the German naval base of Wilhelmshaven in 1945.

The Poles had few forces left in the East to defend when the USSR invaded on 17 September.

The Polish government and high command left the country for Romania and ordered the army to follow. About 85,000 troops escaped to Romania. Most of the government were interned, but 40,000 troops and some politicians escaped to France. 19,000 soldiers made it to Britain in 1939.

Polish military casualties in 1939 were 200,000, a third of them dead and the rest wounded. The Germans took 640,000 prisoners. The officers remained PoWs for the duration of the war, but the other ranks were employed as forced labourers. The Soviets took 240,000 prisoners.

The German policy was to make Poland into an intellectual desert, with a pool of labour that would receive only a very basic education. They killed or imprisoned many intellectuals and priests.

The main difference in the part of Poland occupied by the USSR in 1939 was that education continued, albeit in Belarussian or Ukrainian and with a big political content. They imprisoned 10% of the population, targetting anybody who had been active in the Polish state, whether as a politician or a government employee. They murdered 15,ooo Polish officers at Katyn and elsewhere.

A single resistance body, initially called the ZWZ (Union for Armed Struggle in English) and later the AK (Home Army), was established. An underground government of all political parties was set up. Attempts to extend the network to the Soviet occupied area were made but ran into the problem that the NKVD was more efficient than the Gestapo.

The Germans annexed part of Poland, establishing the General-Government in the rest of their occupation zone. Poles were expelled from the annexed territories to the General-Government; Jews went  to the Lodz Ghetto, which was inside the annexed area. The Poles took revenge by expelling Germans from Poland in 1945. Poland then lost the territory taken by the USSR in 1939, but was compensated with parts of eastern Germany.

There was some collaboration with the Germans at a low-level but none at a political level. Some Poles obtained jobs with the local administration as this protected them from being deported for slave labour. Others were conscripted into the German army and deserted as soon as they could in order to join the Allies.

The Soviets deported a million Poles to the east. Victims were selected for political reasons. Both the Soviets and the Germans gave deportees little notice. Poles expelled by the Germans were given little time to pack, and were sometimes expected to leave their homes clean and tidy for their new German occupants.

After the Germans invaded the USSR in June 1941 Poland and the USSR signed an agreement. The 1939 territorial changes were annulled and diplomatic relations restored. Poles deported to the USSR were given an amnesty, although they had committed no crimes, and a Polish army was established on Soviet soil.

Poles made their way from labour camps and collective farms to the new Polish army. Most were in poor health, and many died along the way. There was a shortage of officers because many had been murdered by the NKVD. The army was eventually evacuated to Iran, where it was supplied by the British. Many civilians accompanied it; they were sent to various parts of the British Commonwealth or to Mexico.

In 1942 the Germans proposed deporting 30 million Slavs, including 85% of Poles, east. The rest of the Poles would be Germanised. 200,000 blue-eyed, blond children were taken from their families and sent to Germany and Austria. Only about 20% returned home after the war. This great tragedy was overshadowed by the even greater tragedy of the Holocaust.

The first of 400 ghettos was set up in October 1939, and mass shootings began when the Germans invaded the USSR in June 1941. These did not reduce the Jewish populations quickly enough, so the death camps were set up. Most Polish Jews died in the four purpose built camps of Belzec, Chelmno, Sobibor and Treblinka.

The vast majority of those sent to these camps were murdered in the gas chambers on arrival, with only a small number of Jews being kept temporarily alive in order to provide the slave labour to operate the gas chambers and burn the corpses. Only 110 Jews survived these camps. Auschwitz and Majdanek were combinations of concentration and death camps, where a higher proportion of Jews were initially selected for slave labour rather than immediate death, and not all the inmates were Jews.

The systematic murder of the Polish Jews began in mid 1942 and was largely over by the end of 1943. By then, the only Jews left in Poland were either slave labourers, including the inhabitants of the Lodz Ghetto, or in hiding.

It was difficult for Polish Jews to find help in escaping, as 80% of them were unassimilated, and Poland was the only occupied country where the penalty for helping Jews was death. Despite this, Zegota in Poland was the only government sponsored scheme to help Jews in occupied Europe.

It took 100 helpers to save one Jew, whilst one collaborator could betray a 100 Jews. The people named as The Righteous Amongst the Nations by Yad Vashem in Israel include over 6,000 Poles, but far more helped Jews. A few Jews collaborated; one of their tactics was to speak Yiddish in public in order to trick Jews into revealing themselves.

Jews resisted, including breaking out into forests and revolts in the Sobibor and Treblinka death camps and the Warsaw Ghetto.

The Polish government-in-exile in London commanded two corps and the AK. The Poles made a major contribution to the war in the air, most famously in the Battle of Britain, where 303 Squadron shot down more enemy aircraft than any other fighter squadron.

The 1 Corps included the afore-mentioned 1st Armoured Division and a parachute brigade. The latter unit was originally earmarked for operations in Poland, but was sent to Arnhem. Its commander, General Stanislaw Sosabowski, was unfairly criticised by General Frederick Browning, the commander of the 1st British Airborne Corps, after the operation failed. Sosabowski was later praised in the memoirs of General Robert Urquhart, commander of the 1st Airborne Division.

The 2 Corps, commanded by General Wladyslaw Anders, was made up of the men who had been captured by the USSR in 1939 and then moved to the Middle East. It fought in Italy, including at Monte Cassino. Most of its members came from the eastern parts of Poland, which were annexed by the USSR in 1945. Few of them returned to Poland after the war.

Poles made a major contribution to Allied intelligence, including the first success in breaking the Enigma code. The Germans knew that an early version of it had been cracked, and tortured four captured Polish code-breakers in order to discover if the current code had been broken. It had, but the Poles insisted, even under torture, that it had not. The Poles also provided intelligence on the German scientific research site at Peenemunde, the V2 rocket and the German plan to invade the USSR in 1941.

Poland broke off diplomatic relations with the USSR after the bodies of the Poles murdered at Katyn were discovered. It had little say in the decision taken by the Big Three of Churchill, Roosevelt and Stalin. Stalin wanted eastern Poland, but was prepared to give Poland some German territory in return.

The Soviets formed the 1st Polish Army in 1943 from Polish PoWs who had not moved to the Middle East and Soviet officers. It was commanded by General Zygmunt Berling, a Polish officer who had refused to follow Anders to the Middle East. Its first battle at Lenino took place in October 1943, before Anders’s 2 Corps had been in action in the Middle East.

The AK had 400,000 members. A general uprising, called Operation Tempest, was planned in order to liberate Polish territory ahead of the advancing Red Army. The AK liberated Vilna and Lvov, but its members were conscripted into the Red Army when it arrived.

In 1943 a political body called the ZPP (Union of Polish Patriots) was formed in the USSR. It was dominated by Communists. In July 1944 the PKWN (Polish Committee of National Liberation) was established as a rival administration to the Polish government-in-exile in London. It was based in Lublin from 1 August, so was known as the Lublin Committee.

Also on 1 August, General Tadeusz Bor-Komorowski (Bor was his code-name and Komorowski his surname), the leader of the AK, launched the Warsaw Uprising. He thought that the Red Army was about to enter the city.

There were 50,000 members of the AK in Warsaw, but only 10% were armed. The German responded brutally to the uprising; 40,000 civilians were killed in one day. Stalin refused to give support to the AK. Only one US air supply mission was allowed to land on Soviet territory; other Allied air missions suffered heavy casualties and only 50% of the supplies dropped reached the AK.

The 1st Polish Army was ordered not to the cross the Vistula and join in the fighting. It made an attempt to do so in September, which resulted in Berling being removed from command.

Fighting ended on 2 October; most of the AK survivors were treated as PoWs, but the Germans destroyed Warsaw. The Red Army did not enter it until 17 January 1945.

A government recognised by the UK, USSR and USA was formed in 1945; it included representatives of the government-in-exile. Elections in 1947 were rigged, and the government-in-exile continued to exist in London until 1990. A referendum was held in 1946, with three questions. The official results showed majorities in favour of all three. However, in Krakow, where the elections were fair, around 85% supported the recommendation of the main anti-Communist party, the Polish People’s Party, and opposed the first question.

Dr Kochanski concluded by saying that Poland was the only Allied country to lose World War II.


Filed under Political History, Reviews, War History