when were u boats first used in ww1
U-boat On 5 September 1914, HMS Pathfinder was sunk by SM U-21, the first ship to have been sunk by a submarine using a self-propelled torpedo. On 22 September, U-9 sank the obsolete British warships HMS Aboukir, HMS Cressy and HMS Hogue (the "Live Bait Squadron") in a single hour.
Aviation in World War I The month of April 1918 began with the consolidation of the separate British RFC and RNAS air services into the Royal Air Force, the first independent air arm not subordinate to its national army or navy. By the end of April the new Fokker, Pfalz and Roland fighters had finally begun to replace the obsolescent equipment of the Jagdstaffeln, but this did not proceed with as much dispatch as it might have, due to increasing shortages of supplies on the side of the Central Powers, and many of the Jastas still flew Albatros D types at the time of the armistice. The rotary engined Fokker D.VIII and Siemens-Schuckert D.IV, as well as surviving Fokker Triplanes, suffered from poor reliability and shortened engine life due to the Voltol-based oil that was used to replace scarce castor oil – captured and salvaged Allied aircraft (especially Sopwith Camels) were scrounged, not only for engines and equipment, but even for their lubricants. Nonetheless, by September casualties in the RFC had reached the highest level since "Bloody April"[28] – and the Allies were maintaining air superiority by weight of numbers rather than technical superiority.
World War I The trigger for the war was the assassination of Archduke Franz Ferdinand of Austria, heir to the throne of Austria-Hungary, by Yugoslav nationalist Gavrilo Princip in Sarajevo on 28 June 1914. This set off a diplomatic crisis when Austria-Hungary delivered an ultimatum to the Kingdom of Serbia,[11][12] and entangled international alliances formed over the previous decades were invoked. Within weeks, the major powers were at war and the conflict soon spread around the world.
American entry into World War I On December 7, 1917, the U.S. declared war on Austria-Hungary.[5][6]