At the outset of World War One, German U-Boats were not very effective. Although they caused the officers of the British Royal Navy to become rather paranoid of them, they remained ineffective when it came to blockading of Britain. The primary reason this was the case were the prize rules. The prize rules were a series of international agreements that stated that merchant ships could not be fired upon without warning; merchant ships could be sunk by enemy ships if and only if the crews would be taken aboard or they could get to shore on their own via lifeboat. The prize rules were written without submarines in mind; the confined spaces of submarines allowed for no excess passengers, and the principle advantage of the submarine was the element of surprise. By and large, Germany followed these rules throughout 1914.
In 1915, however, the prize rules were abandoned. Germany believed that Britain was violating certain naval agreements, so they needed not to worry about the prize rules. Unrestricted submarine warfare was thus begun, and it was a huge success for Germany; hundreds of thousands of tons of Allied ships were sunk each month. It should be noted, Germany, although having a policy of unrestricted submarine warfare, did not want to bring neutral powers into the war. Germany went so far as to print warnings in major newspapers of neutral powers warning against boarding certain ships, such as an advertisement printed in the New York Times.
On May 7, 1915, a German U-Boat sank the passenger ship RMS Lusitania. In the attack, 1,198 were killed, 128 of them American. The United States was outraged; in order for to quell the outrage, Germany agreed to not attack passenger ships. Much more care was taken in what ships were attacked, however, the care Germany took was not enough. The sinkings of the Arabic on August 19, 1915 and the Sussex on March 24, 1916, with the latter attack killing fifty Americans, nearly pushed the isolationist United States into war. President Woodrow Wilson thus issued to Germany an ultimatum, either Germany immediately stop their unrestricted submarine warfare, or the US would enter the war on the Allied side. Chancellor Bethmann-Hollweg of Germany, backed down, he feared Germany could not deal with another power. Many of the Generals of the Kriegsmarine believed Bethmann-Hollweg was in error, in 1917, however, as Germany grew weaker, they had their way.
By 1917 Germany’s offensive on the Western Front had been stalled, by all accounts, it appeared that Germany would lose the war. German military leaders estimated, that by the resumption of unrestricted submarine warfare, 600,000 tons of Allied vessels could be sunk per month, bringing Britain to starvation within six months. The risk associated with this plan however, was that of bringing the United States into the war. Although this was a valid concern, the US was not prepared for war, it would take several months of preparation, by which time Britain would already be defeated. It was on this gamble that Field Marshall von Hindenburg and General Ludendorff submitted their proposal to Chancellor Bethmann-Hollweg and unrestricted submarine warfare was reinitiated on Febuary 1, 1917.
By April, the future was bleak for Britain, even Lord Jellicoe himself believed that Britain would be defeated. However, the convoy system was initiated in the nick of time. On the verge of starvation, convoys allowed Britain to recover splendidly. The resumption of unrestricted submarine warfare coupled with the Zimmermann telegram pushed the US to war; the US would now enter the war with Britain still fighting. Germany’s bet had failed and they were doomed to lose World War One.
Ultimately, Germany’s gamble did not pay off, but it was one which they had to take. At the turn of 1917, Germany was left with few options; their various assaults on the Western Front were deadlocked and only sapped away at their resources. It appeared that they were slowly losing the war. The resumption of submarine warfare was done in the hopes that Great Britain could be defeated before the United States could mobilize and deploy troops. Had convoys not been implemented when they were most needed in May 1917, Germany’s bet would have probably paid off. Lord Jellicoe himself, in April 1917, said “It is my firm conviction that we shall lose the war by the starvation of this country,” however, it was the convoy that Jellicoe and the Germans had failed to take into account; because of it, Germany’s final gamble did not pay off, Britain was not defeated, the US entered the war, and Germany was in a worse position than before.