Before the US Navy eclipsed the Royal Navy one of the closest threats to the Royal Navy's dominance of the high seas was the German U-boats of WWI. The German Naval program started in 1898 by Alfred Von Tirpitz quickly created the second largest navy in the world second only to the Royal Navy. Using one of the most advanced submarine programs the Germans were able to successfully change strategies of luring capital ships toward subs to using submarines against more vulnerable merchant shipping.

When the Germans were starting to break the English's supply chain with submarines the USA placed an ultimatum that if the Germans did not halt their unrestricted submarine program the US would declare war on Germany.

Had the Germans ignored this request they could have starved the British out. With anti-submarine warfare in its infancy - resorting to ramming being most popular among captians.

Why did the Germans wait until it was too late to reinstate their unrestricted submarine warfare in WWI?

  • 3
    Plainly: Fear of American retaliation, and entry to the war. Aug 21, 2013 at 22:10
  • @Pieter Geerkens What could the Americans do to stop the U-Boat strangulation of the British as far as material, strategies and tactics? It's my understanding that early anti-submarine tactics revolved around disguised merchant ships with deck guns and ramming subs with destroyers. Aug 21, 2013 at 22:33

4 Answers 4


Plainly: Fear of American retaliation, and entry to the war.

Why? Because the US very nearly entered the war in 1915 in retaliation for the sinking of Lusitania; Only Germany's pull-back from unrestricted submarine warfare kept the US out for two more years (or at least such was believed in German high command:

A German decision on 9 September 1915 stated that attacks were only allowed on ships that were definitely British, while neutral ships were to be treated under the Prize Law rules, and no attacks on passenger liners were to be permitted at all.[66][67]

It was in the interests of the British to keep US passions inflamed, and a fabricated story was circulated that in some regions of Germany, schoolchildren were given a holiday to celebrate the sinking of Lusitania. This story was so effective that James W. Gerard, the US ambassador to Germany, recounted it in his memoir of his time in Germany, Face to Face with Kaiserism (1918), though without substantiating its validity.[68]

Almost two years later, in January 1917 the German Government announced it would again conduct full unrestricted submarine warfare. This together with the Zimmermann Telegram pushed US public opinion over the tipping point, and on 6 April 1917 the United States Congress followed President Wilson's request to declare war on Germany.[69]

see more here: http://en.wikipedia.org/wiki/RMS_Lusitania

  • Thanks for the answer. Do you think the U-Boat blockade could have succeeded even with an American entry into the war? Aug 22, 2013 at 15:21
  • Starving out the enemy wasn't a practical strategy for Germany at that stage. France and America couldn't be beaten that way, and England had Germany under a full blockade for the entire war. If it came down to that, Germany would starve first. Indeed, over 400K deaths were attributed directly to the blockade, deaths that starvation/malnutrition and the blockade indirectly contributed to were probably twice that. Germany's only hope at that stage was a military victory that would give them a better bargaining position in peace talks.
    – Odysseus
    Aug 23, 2013 at 0:28
  • 1
    @AndrewKloos: Or, more succinctly: "Because they didn't realize it was already too late." You are applying 20-20 hindsight to the question. Aug 31, 2013 at 14:29
  • 2
    Starving out the enemy was a perfectly practical strategy which very nearly worked. Starving out Britain would have been enough to win the war, since Britain, France, and Russia together were barely able to hold the Germans back. Also, 400k is the total figure for excess German civilian mortality during the war years, not the figure "attributed directly to the blockade." Sep 10, 2013 at 23:13

The US ultimatum threatened war unless Unrestricted submarine warfare was abandoned.

A war can be won either by crashing an opponent on the battlefield or by strangling it economically. Submarine warfare is the strangulation approach. I.e., when applying it, one has to calculate long term effects. The pro of unrestricted submarine warfare is a better blockade of Britain (and France). The contra is the addition of the resources of the USA to the already formidable combination of Britain, France and Russia.

The German General Staff decided that in 1915 the costs were larger than the benefits.


Basically, it was a race between the effects of unrestricted submarine warfare (USW) and U.S. intervention (USI).

If USW had been instituted earlier, the Germans would have come closer to starving out Britain. But USI would also have happened earlier, with the U.S. providing more food to Britain, and soldiers on the Western front earlier.

Given that the Germans did not come as close to winning the war by starving out Britain as by the 1918 "superoffensive," a case could be made that USW was resumed too early. If it had been deferred until say, early 1918, maybe the Americans would have been ready to arrive in France in force only in 1919, after the Germans won the war in 1918.

  • once convoys were implement the threat of U-boats was basically over. If the U boats had done better sooner, the British would have turned to convoys sooner.
    – pugsville
    Mar 2, 2016 at 12:00

The U-boat of WWI was not nearly the weapon that it became in the next war. Holger Herwig documented the limitations of the U-boat in his book The First World War: Germany and Austria-Hungary 1914-1918. U-boats were primitive and prone to various failures. The means of radio communication with a submerged vessel were still underdeveloped. Germany had no answer for the convoy.

The Germans did not have the resources to fight a two-front war and build an effective submarine fleet. In 1917 they were only able to keep at most 30 subs on station west of Britain at any time.

The German U-boat did not threaten the British lifelines. Herwig documents the countermeasures that Britain implemented, including rationing and setting insurance rates to prevent a breakdown in world maritime trade.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.