Germany had a weak navy (weak battlefleet). Nations with strong navies could conduct Guerre de Escadre (fleet actions); nations with weak navies had to revert to Guerre de Course (merchant warfare).
Underseaboats.
Submarine warfare is a military tactic used by many nations where submarines are used to attack enemy ships or as a direct deterrent. This was used extensively by the Germans during World War II.
During WW2, all the major countries involved used submarines.
In almost all navies during WWII, submarines were called "boats"...not ships. In Germany, a sub was called an "under-sea-boat", with German enthusiasts preferring to use the German spelling/pronunciation of "boot" for boat. Bottom line: "U-Boat submarine warfare..." is simply submarine warfare (Sub Warfare is what most boys in America grew up calling it).
Submarine warfare was abhorrent in the US during WW1. The British sank US ships trying to enter blockaded German ports. The same is true of US ships trying to enter blockaded British ports. However the Germans use submarine warfare to sink a USS Lusitania. That was the tipping for the US. Prior to then we were not wanting to get into "entangling alliances.
The Uboat was a submarine made by the Germans
During the Treaty of Versailles
What political group wanted to take power in Germany during WW1.
Most likely Germany, they had the U-boats (underwater boats)
Gas was first used in warfare during the Second Battle of Ypres in 1915 by the Germans.
The Germans faced France and French colonial forces, Britain and Britich colonial forces, and, eventually, the Americans on their Western Front in trench warfare. Austrian and Germans faced the Russians for a time on the Eaastern Front, some of that in trench warefare.
In WW1, the German policy of unrestricted submarine warfare irritated neutral nations such as the United States and eventually helped public opinion to support the US entry into the war. In WW2 the German policy of unrestricted submarine warfare in the Atlantic irritated nominally neutral nations such as the United States and provided a rationale for increasing US support of Britain and its allies. In WW2 the American policy of unrestricted submarine warfare in the Pacific probably contributed to the degradation of Japanese economic capabilities as the war progressed.