In 1914, like every other country that possessed them, Germany and Austria-Hungary viewed their small submarine fleet as an augmentation of their main surface fleet. Submarines were to be used to scout the enemy and pick off any warships they could find. German U-Boats had well publicized successes in these endeavors early in the war. However, they soon realized that the British blockade would starve Germany if something wasn't done to counter it. The German fleet was too weak to face off against the British. The only opportunity to actually attack the enemy soon became the use of the u-boat to institute a counter-blockade against shipping in the British Isles.
The Germans and Austrians started to assault Allied and neutral shipping with dire diplomatic consequences to their relations with the US and other key neutral nations. The Germans had bet all on their U-boats' success. They wagered their war and their nation on a few hundred frail craft manned by a few thousand men. The U-boats would come close to victory if one looks at tonnage sent to the bottom, but it would never be enough to starve Great Britain out of the war and defeat the substantial Allied countermeasures poised to blunt the Germans’ chosen instrument.
As with other technology introduced in World War I, the German u-boat’s capabilities would advance with faster and deadlier models coming out as the war dragged on. The Germans also developed a long range submarine arm made up of imperfect and underpowered craft that nonetheless spread the havoc of the submarine war to far flung nations who knew little or nothing of the ravages of the First World War.
Photos courtesy of the Marist College Special Archives and Collections from the Lowell Thomas papers