German Torpedo Boats of World War I — A Roads Classic

The German torpedo boats of World War I were designed to execute torpedo attacks on bigger warships. While other nations like Britain started to increase the size and gun armament of their torpedo boats — or torpedo boat destroyers — and designed a ship that would later just be called "destroyer", the German Navy stayed with the idea of small craft that were to focus on their torpedoes as their main weapons.

Action

During the war, it became obvious that the artillery component of those boats had to be increased. Therefore, all torpedo boat classes laid down during wartime got more and larger guns — the climax were the large torpedo boats ("Große Torpedoboote") of the Design 1916 — with their four 15cm guns. At  over 2000 tons they were the biggest and most powerful ships of their kind at the end of the war. They were in many ways the equivalent of the contemporary destroyers in other navies (they were often referred to as such by their crews). 

Torpedo Boat G-136 at Sea

The combat effectiveness of the German torpedo boat squadrons, however, was not very impressive. In an early, October 1914, action off the Dutch coast, a British flotilla consisting of a light cruiser and four destroyers sank an entire squadron of torpedo boats causing German commanders to lose confidence in the vessels. As a direct result, there were very few further sorties into the Channel and the torpedo boat force was relegated to coastal patrol and rescuing downed pilots for fear of similar losses. Consequently, it is difficult to find accounts of the boats sinking Allied ships. The sinkings of a British minelaying sloop and a single destroyer, were all the editors could find

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A Flotilla in Port

Germany built over 300 torpedo boats by the end of World War I, and 67l of them were lost because of enemy actions. Fifty of the most  modern ones were interned in Scapa Flow and scuttled there in June 1919; only a few of them were not sunk. Of the 114 boats left in Germany, only 24 were allowed to be kept after the Treaty of Versailles, but most of the remaining boats were of such a bad condition that it was difficult to keep even 24 of them running. Most of those boats were later reconstructed and several of them were even used for auxiliary duties during World War II.

Sources: german-navy.de/; http://www.naval-history.net/; Wikipedia