Tag Archives: merchant ships

Victory over the U-boats

On 21 October 1918 Admiral Reinhard Scheer, the German Chief of the Admiralty Staff, ordered all U-boats to return to base. This ended the German campaign of unrestricted submarine warfare, which meant sinking merchant ships without warning, that had begun on 1 February.[1]

Scheer’s orders were obeyed by almost all U-boat captains. UC 74 (Oberleutnant Hans Schüler) sank the 85 ton Greek sailing ship Aghios Gerasimos by gunfire in the Eastern Mediterranean on 23 October and a number of merchant ships were sunk by mines laid by UC 74 after 21 October off the Suez Canal. Other ships were sunk after 21 October by mines laid earlier.[2]

Admiral Henning von Holtzendorff, Scheer’s predecessor, had argued that the Germans had to break the British economy in order to win the war and this could be achieved by destroying 600,000 tons of merchant shipping per month for five months, which would cut British trade by 39% within five months. The Germans were aware that this might bring the USA into the war against them but thought that it would not be able to replace the lost merchant shipping and that there would be insufficient transports to take US troops to Europe.[3]

The U-boats’ best month before February 1917 was October 1916, when they sank 341,363 tons of merchant shipping according to German records. There are some differences between British and German figures but they are not large. German ones are slightly higher over the whole war but are lower in some months. V. E. Tarrant argues that the German numbers are the more accurate and they are quoted here.[4]

As shown in the table below, the Germans achieved their target of sinking 600,000 tons of shipping in only three months: April, May and June 1917. However, the 860,334 tons sunk in April meant that the average for the first seven months of unrestricted submarine warfare was 612,310 per month. Von Holtzendorff’s belief that this level of loss for five months would break the British economy was proved to be wrong.

These figures are for ships from all countries, not just Britain sunk by U-boats, including by mines laid by U-boats, but excluding ships sunk by surface raiders and aircraft.

Month Gross tons
Oct-14 866
Nov-14 2,084
1914 Total 2,950
Jan-15 17,577
Feb-15 22,785
Mar-15 89,517
Apr-15 41,488
May-15 126,895
Jun-15 115,291
Jul-15 98,005
Aug-15 182,772
Sep-15 136,048
Oct-15 86,064
Nov-15 167,523
Dec-15 107,739
1915 Total 1,191,704
Jan-16 49,610
Feb-16 95,090
Mar-16 160,536
Apr-16 187,307
May-16 119,381
Jun-16 93,193
Jul-16 110,728
Aug-16 163,145
Sep-16 231,573
Oct-16 341,363
Nov-16 326,689
Dec-16 307,847
1916 Total 2,186,462
Jan-17 328,391
Feb-17 520,412
Mar-17 564,497
Apr-17 860,334
May-17 616,316
Jun-17 696,725
Jul-17 555,514
Aug-17 472,372
Sep-17 353,602
Oct-17 466,542
Nov-17 302,599
Dec-17 411,766
1917 Total 6,149,070
Jan-18 295,630
Feb-18 335,202
Mar-18 368,746
Apr-18 300,069
May-18 296,558
Jun-18 268,505
Jul-18 280,820
Aug-18 310,180
Sep-18 171,972
Oct-18 116,237
Nov-18 10,233
1918 Total 2,754,152
Grand Total 12,284,338

Source: Tarrant, V. E., The U-Boat Offensive, 1914-1945, (London: Arms and Armour, 1989), pp. 152-53. Originally from Der Krieg zur See, 1914-15, vol v: Der Handelskreig mit U-booten.

The losses were stemmed by the adoption of various counter-measures of which the introduction of convoys was the most important. Convoys had been used in previous wars and for troopships in this one. The Admiralty opposed them for a number of reasons:

Code breaking and radio direction finding could enable it to track U-boats. This had worked against surface raiders but was ineffective against U-boats because they could not be detected once submerged except by spotting their periscopes or torpedo tracks

An armed merchantman could avoid torpedo attack by zigzagging and fight off a gun attack by a surfaced U-boat.

Merchantmen would not be able to keep station, especially at night. In fact convoys were in areas where U-boat attack was unlikely for most of their journeys, giving them time to practice formation sailing.

Ships would be delayed in sailing. This was false as ships were already delayed by reports of U-boats near their ports.

Convoys would give U-boats an attractive target as they assembled in open seas. The US entry into the war meant that they could assemble in US ports. They could in any case have done so at Bermuda or Halifax, Nova Scotia.

Convoys would concentrate targets together, so would require to be escorted by as many as one destroyer per merchant ship. Allocating this number of destroyers to convoy escort would mean that the Grand Fleet would have to stay in port. Only eight to 10 escorts were actually needed for a 20 ship convoy and smaller ships than destroyers proved to be adequate convoy escorts.[5]

It was actually almost as hard for a U-boat to spot a convoy as it was for it to find an independent ship. According to Vice Admiral Sir Arthur Hezlet, a British WWII submarine captain, a ship could be spotted from 10 miles away. A 20 ship convoy would be two miles wide so could be seen from 11 miles away. Convoys therefore meant that U-boats would find fewer targets, not more. Even if a U-boat spotted a convoy, it would probably have time to  torpedo only one, at most two of its ships and would be counter attacked by the escorts. The British also used radio direction finding to avoid U-boats.[6]

This was confirmed by Karl Dönitz, commander of Germany’s U-boats in WWII and a U-boat captain in WWI. He wrote that ‘[t]he oceans at once became bare and empty…for long periods…the U-boats…would see nothing at all.’ When a convoy did appear, the ‘U-boat might well sink one or two of the ships, or even several; but that was but a poor percentage of the whole.’[7] It would also be vulnerable to counter-attack by the convoy’s escort.

The British had been using convoys in the war. As well as troopships, ships sailing between England and the Netherlands had been convoyed since July 1916 because of the risk of destroyer attack. Ships carrying coal from Britain to France were convoyed from February 1917 at the request of the French. The Admiralty insisted on calling the convoys controlled sailings.[8]

The French coal convoys had been organised by Commander Reginald Henderson.[9] He obtained figures from the Ministry of Shipping that showed that the number of ocean going ships sailing to and from the UK was much lower than realised.

The Admiralty had included short voyages made by small, coastal ships in its reports of the number of ships calling at British ports in order to make the Germans think that the sea traffic to the UK was too great for the U-boats to destroy. The 2,500 voyages each way per week claimed was too many to convoy but the true number of ocean going ships arriving and leaving was 120 to 140 per week.[10]

On 25 April 1917 the War Cabinet decided that the Prime Minister, David Lloyd George, should visit the Admiralty in order to find out what it was doing about U-boats. Lloyd George and his colleagues were in favour of convoys but the Admirals had resisted them. However, the next day Vice Admiral Alexander Duff, head of the Admiralty’s Anti-Submarine Division, who now had Henderson’s figures, submitted a paper to the Admiralty stating that ‘[i]t seems to me evident that the time has arrived when we must be ready to introduce a comprehensive scheme of convoy at any moment.’[11]

Convoys would need 70 escorts. Only 30 destroyers were currently available but more would be built by the time that convoys could be fully organised and USN ships would soon be available.[12]

The introduction of convoys did not eliminate shipping losses but it reduced them sharply, from 5% of sailings in the UK in April 1917 to 0.5% by the end of the war. Some ships continued to sail independently and suffered heavy losses.[13]

A large number of aircraft were allocated to anti-submarine warfare in home waters: an average of 189 aeroplanes, 300 seaplanes and 75 airships in the last six months of the war, with an average of 310 being available each day. Their bombs were too small to sink U-boats but they had a significant deterrent effect. In 1918 U-boats attacked only six convoys with air escorts, sinking only three ships. Over the whole war only five ships were sunk in convoys with both air and surface escort.[14]

The Americans and British were also able to build new ships more quickly than the Germans had forecast. The US entered the war with a relatively small shipbuilding industry but rapidly built one, including constructing accommodation for workers and public transport to take them to work. The British made the Admiralty responsible for both naval and merchant shipbuilding, so that it could make the necessary trade-offs. These including suspending construction of three of the four Hood class battlecruisers in order to build more merchantmen. Sir Eric Geddes, a businessman who had solved railway supply problems behind the Western Front was made Controller of the Admiralty, putting him in charge of the materiel side of the navy. This job was normally done by the Third Sea Lord, an admiral. Ships were built to standardised design.[15]

Merchant shipping construction (tons)

1915 1916 1917 1918
UK          1,000,000         600,000          1,800,000   2,400,000
USA             250,000  n/a          1,500,000   4,500,000

Source: Friedman N., Fighting the Great War at Sea: Strategy, Tactics and Technology (Barnsley: Seaforth, 2014), pp. 284-86.

About 1,700,000 tons of Austrian and German merchant shipping interned in US ports were requisitioned by the US government. They included a number of liners, which transported US troops to France. Amongst them was the giant Vaterland, renamed the Leviathan in US service.[16]

The U-boats failed to stop over 2,000,000 US soldiers sailing to Europe, 10% of them on board the Leviathan. Two eastbound troop transports were sunk by U-boats and another accidentally by collision. Three returning to the USA to collect more troops were also sunk. The total of US soldiers killed by U-boats was less than the 700 who died as a result of influenza caught on the voyage.[17]

German U-boat construction in 1918 was only able to keep pace with losses. They had 224 [Sondhaus] or 226 [Gibson and Prendergast] under construction at the end of the war and completed 13 in October 1918. The hoped to complete 30 a month in 1919. However, they were struggling to man their new boats. U-boats needed experienced captains and fully trained crew: the six most successful U-boat captains in terms of tonnage sunk and 14 of the leading 18 survived the war. Consequently, the Germans refused to cut the training programme given to men before they were assigned to an active U-boat. About two dozen of those under construction at the end of the war could have been commissioned had trained personnel been available.[18]

The U-boats inflicted severe damage to Allied shipping but their attempt to blockade the UK failed and brought the USA into the war against Germany.


[1] L. Sondhaus, German Submarine Warfare in World War I: The Onset of Total War at Sea (Boulder MD: Rowman & Littlefield, 2017). Kindle edition, location 4855.

[2] Ibid. Kindle locations 4861-68.

[3] 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).

[4] V. E. Tarrant, The U-Boat Offensive, 1914-1945 (London: Arms and Armour, 1989), pp. 152-53.

[5] N. Friedman, Fighting the Great War at Sea: Strategy, Tactics and Technology (Barnsley: Seaforth, 2014), pp. 274-78.

[6] Original source A. R. Hezlet, The Submarine and Sea Power (London,: 1967), pp. 94-95; Quoted in 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 v, pp. 88-89.

[7] Original source K. Doenitz, Memoirs: Ten Years and Twenty Days (London,: 1959), p. 4;  Quoted in Marder, From. vol. v, p. 89.

[8] Friedman, Fighting, pp. 276-77.

[9] C. E. Fayle, Seaborne Trade, 3 vols (London: HMSO, 1920). vol. iii, p. 100.

[10] J. S. Corbett, H. Newbolt, Naval Operations, 5 vols (London: HMSO, 1938), p. vo. v. p. 18.

[11] Ibid. vol. v, p. 19.

[12] Ibid. vol. v, pp. 18-19.

[13] Marder, From. vol. v, p. 87.

[14] Ibid. vol. v, pp. 91-93.

[15] Friedman, Fighting, pp. 284-86.

[16] Ibid., p. 286.

[17] P. G. Halpern, A Naval History of World War I (London: UCL Press, 1994), p. 437.

[18] R. H. Gibson, M. Prendergast, The German Submarine War, 1914-1918 (London: Constable, 1931), p. 363; Sondhaus, German. Kindle locations 4497-4513.



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SS Sussex Torpedoed by U-Boat 24 March 1916

In February 1916 Germany announced that from 1 March its U-boats would sink defensively armed British merchant ships without warning. Germany had, under pressure from the USA, abandoned unrestricted submarine warfare in September 1915. The Germans claimed that British defensively armed merchantmen had been ordered to attack U-boats before being attacked themselves, so could not be regarded as acting defensively. The Admiralty quickly disproved this accusation by publishing the actual orders.[1]

The German position on the issue of unrestricted submarine warfare is described by Paul Halpern as being ‘somewhat confusing’.[2] The naval and military commanders wanted to pursue unrestricted submarine warfare but Kaiser Wilhelm and Chancellor Theobald von Bethmann Hollweg were concerned about US opinion. The US government opposed the treatment of armed merchant ship as warships.

Following a conference on 4 March the Kaiser accepted that unrestricted warfare was necessary, with a likely start date of 1 April. Until then, Bethmann Hollweg should attempt to persuade the Americans to accept the German view. In the interim U-boats were authorised to sink enemy merchant ships in the war zone and armed ones outside it. Passenger liners, whether armed or not, could not be attacked anywhere by submerged U-boats. Halpern describes this as ‘sharpened’ rather than unrestricted submarine warfare.[3]

Admiral Alfred von Tirpitz, the architect of the German battlefleet had not been invited to the 4 March meeting. He resigned as State Secretary of the Imperial Naval Office, a job mainly concerned with administration and naval building, soon afterwards.

The Germans had 52 U-boats in March 1916, compared with 29 or 30 when they began unrestricted submarine warfare a year before. Of these 16 were in the North Sea, 20 small and short ranged ones with the Flanders Flotilla, 4 in the Baltic, 7 in the Adriatic and 5 at Istanbul. It was expected that another 38 would be completed by August.[4]

Several Dutch merchant ships were sunk in March, including the 13,911 liner Tubantia, the largest neutral ship sunk during the war. The Dutch were angered by these losses, but the attitude of the USA was far more important to the Germans.[5]

On the afternoon of 24 March the 1,353 ton French packet Sussex was torpedoed and badly damaged by UB29 (Oberleutnant Herbert Pustkuchen) whilst making her regular run from Folkestone to Dieppe with over 325 passengers. The Germans claimed at first that she had hit a mine, but fragments of a torpedo were found after she had been towed into Boulogne.[6]

The 50 dead included some of the 25 Americans on board. Pustkuchen claimed that he assumed from her crowded decks that she was a troopship.[7] British troopships then crossed at night between Folkestone and Boulogne.[8] The Germans may not have known that and Pustkuchen, with the very limited view offered by a periscope, may have genuinely thought that he was firing at a troopship. His action, however, created a major diplomatic incident with the USA.

On 19 April US President Woodrow Wilson told Congress that that unless the Germans abandoned ‘their present method of warfare against passenger and freight-carrying vessels, the Government have no choice but to sever diplomatic relations with the German Government altogether.’[9]

On 20 April the Germans agreed to stop sinking merchant ships without warning. Four days later Admiral Reinhard Scheer, the recently appointed C.-in-C. of the High Seas Fleet, recalled all his U-boats from the North Sea on the grounds that there was no point in sending boats on dangerous missions when their actions were so restricted. This left only the short ranged boats of the Flanders Flotilla operating against Allied shipping in British waters.[10]

The following table shows Allied shipping losses to U-boats since the end of the period of unrestricted submarine warfare. Sinkings rose in April and May and then fell again, especially outside the Mediterranean, to which several U-boats were transferred in September 1915 so that they could raid Allied commerce in an area where the risk of killing Americans was reduced, although not eliminated. On 7 November U38, a German boat that was flying Austro-Hungarian colours because Germany and Italy were not yet at war, sank the Italian liner Ancona, killing over 200 people, including about 20 Americans.[11]

Merchant shipping Losses to U-boats
Total Mediterranean
Month Ships Gross tons Ships Gross tons
Oct-Dec 1915 140 361,326 80 293,423
January 1916 25 49,610
February 1916 44 95,090
March 1916 69 160,536
April 1916 83 187,307
May 1916 63 119,381 37 72,092
June 1916 63 93,193 43 67,125

Source: P. G. Halpern, A Naval History of World War I, (London: UCL Press, 1994), p. 308.

The Germans thought that unrestricted submarine warfare was their best chance of forcing Britain out of the war. However, it also risked bringing the USA into the war on the Allied side. In 1916 they had too few U-boats to achieve the former but pursuing this strategy could still cause the latter.


[1] Naval Staff Monograph (Historical) 1926 vol. xv, Home Waters part vi, October 1915 to May 1916. p. 94.

[2] P. G. Halpern, A Naval History of World War I (London: UCL Press, 1994), p. 305.

[3] Ibid., p. 306.

[4] Ibid.

[5] Ibid., p. 307.

[6] Naval Staff vol. Xv. p. 139.

[7] Halpern, Naval, p. 307.

[8] Naval Staff vol. Xv. p. 139.

[9] Quoted in R. H. Gibson, M. Prendergast, The German Submarine War, 1914-1918. (London: Constable, 1931), p. 88.

[10] Ibid., p. 89.

[11] Halpern, Naval, p. 385.

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The Naval Blockades: (2) Germany

During the First World War both the United Kingdom and Germany attempted to carry out naval blockades of the other. Each country used actions by the other to justify escalations by the other. The Germans laid unanchored, floating mines in the North Sea early in the war. International law said that such mines had to become inoperable after an hour. It was not feasible to do so, but this gave the UK an opportunity to argue that it was Germany that had first broken international law.

The UK then tightened its blockade beyond what was permitted by the 1909 Declaration of London. On 5 November the Admiralty announced that the whole of the North Sea was a war zone, warning that ships entering from the north would do so at their own risk. The official reason for this was the German minefields, but the real one was to force neutral ships heading into the North Sea to go through the English Channel, making it easier to search them for contraband.

On 4 February 1915 Germany announced that the waters round the United Kingdom of Great Britain and Ireland would be a war zone from 18 February. It justified this by reference to the British declaration of 5 November. All hostile merchant ships in this area would be destroyed without warning. The safety of neutral ships could not be guaranteed because British ships had been flying neutral colours. U-boat captains were ordered that their first duty was the safety of their boat, so they should not take risks to find out if a ship was really neutral.[1]

In 1914 the most important successes of German U-boats had been against warships. This continued in 1915, with U24 sinking the pre-dreadnought battleship HMS Formidable in the early hours of the year.

It was extremely difficult for submarines to comply with the rules of cruiser warfare, which required raiders to stop and search enemy merchant ships. Merchant ships could be sunk or captured only if their cargoes contained either war materials (absolute contraband) or items such as food or fuel that had peaceful uses but were intended for the enemy’s military (conditional contraband).

The safety of the crews of merchant ships that were sunk had to be ensured. Submarines had no space for prisoners and no spare men to act as prize crews for captured ships, so could comply with this only if the sinking occurred close to land.

One man had predicted before the war that submarines would sink merchant ships without warning. This was the British Admiral Lord Fisher, who by February 1915 was in his second spell as First Sea Lord. In late 1913 he had written a paper arguing that the invention of the submarine meant that the main threat to the UK was having its food and oil supplies cut off by submarine attacks on its merchant shipping

Winston Churchill, the First Lord of the Admiralty, and Admiral Prince Louis Battenberg, then the First Sea Lord, both refused to believe that any country would use its submarines in such a way. They thought that Fisher’s view that it would be done weakened his arguments about the risk of submarine attack on the UK’s food and oil supplies.[2]

Only four British merchant vessels had been sunk by U-boats before 30 January. In each case the Germans had given the crew time to abandon ship and no lives were lost.[3]

The most controversial incident had come on 26 October when Kapitänleutnant Rudolf Schneider’s U24 torpedoed but did not sink the 4,590 ton French steamer Amiral Ganteaume. She was carrying 2,500 Belgian refugees, 40 of whom were killed. However, Schneider may have thought that she was a troop ship. Whether he did or not, the incident showed the potential political and diplomatic implications of submarine warfare against merchant shipping.[4]

In the Irish Sea on 30 January U21, which had sunk the cruiser HMS Pathfinder in September, the first moving warship ever to be sunk by a submarine, stopped, searched and sank three British merchantmen after allowing their crews time to take to their boats. On the same day, however,  U20 torpedoed and sank three British merchant ships off Le Havre without warning. The crews of the Tokomaru and Ikaria all survived, but all that was found of the 21 man crew of the Oriole was two lifebuoys discovered near Rye on 6 February.[5]

Before the war Kapitänleutnant Ulrich Blum of the Kaiserliche Marine, the German navy, had estimated that 222 U-boats would be needed to successfully carry out a war against British commerce under international law, far more than Germany possessed in early 1915.[6]

The KM began the war with 24 operational U-boats, plus four older ones that were used for training and 16 under construction. By 22 February 13 more had been completed, but one of the new boats and six of the pre-war ones had been lost. Seven newly completed boats were under sea trials, leaving the KM theoretically with 23 to attack British trade. The need to refit, repair and resupply meant that there was an average of 5.6 and a maximum of 12 boats at sea on any one day between March and May 1915.

After the German capture of the Belgian coast gave them bases much closer to the UK, they had begun to build smaller UB and UC coastal submarines. The latter were minelayers, which initially were armed only with mines, although later ones also had torpedo tubes and guns. They were supposed to take four months to build compared with 18 for an ocean going boat, but UB1 was constructed in 75 days. By mid July 1915 17 UBs and 15 UCs had been completed, but the first six UBs were not operational until the latter part of April and UC1 not until early June. [7]

The U-boat war against British trade would eventually cause great problems for the UK, but Germany had too few submarines when it first launched its offensive. However, British counter-measures were also inadequate at first.

The Germans had lost a high proportion of their submarines so far in the war, but two had been rammed by warships whilst on the surface, four had struck mines and the seventh had been sunk by another U-boat on the surface after failing to respond to a challenge. The method that British warships possessed of sinking submerged submarines was the towing of explosive sweeps.

The British had laid a minefield across the Dover Straits in an attempt to stop U-boats entering the English Channel, but 4,000 out of just over 7,000 mines laid between 2 October 1914 and 16 February 1915 drifted or sank to the bottom because the weights holding them in position were too light.[8] The British also laid nets and organised patrols of small, armed ships, but the U-boats were able to pass through the Dover Straits.

The orders issued to U-boat captains on 18 February were that they should attack all hostile ships except hospital ships, unless clearly acting as troopships, and Belgian Relief ships. Neutrals should be spared. However, they were told that ‘if, in spite of the exercise of great care , mistakes should be made, the commanding officers will not be held responsible.’[9]

However, the first ship to be attacked in the new campaign was the Norwegian Belridge, which was carrying a cargo of oil from New Orleans to Amsterdam for the Dutch government. She was torpedoed on 19 February, but managed to make a British port. The Germans apologised and paid compensation.[10]


[1] P. G. Halpern, A Naval History of World War I (London: UCL Press, 1994), pp. 293-94.

[2] R. H. Gibson, M. Prendergast, The German Submarine War, 1914-1918. (London: Constable, 1931), p. 24.

[3] C. E. Fayle, Seaborne Trade., 3 vols. (London: HMSO, 1920). vol. i, pp.358, 365-66.

[4] Halpern, Naval, p. 292.

[5] Fayle, Seaborne. vol. i, pp. 366-68.

[6] Halpern, Naval, p. 291.

[7] V. E. Tarrant, The U-Boat Offensive, 1914-1945 (London: Arms and Armour, 1989), p. 7.

[8] Ibid., p. 17.

[9] Gibson, Prendergast, German, p. 31.

[10] Fayle, Seaborne. vol. ii, p. 12


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