World War I
World War I was a major conflict fought over four years mainly in continental Europe from 1914 to 1918. It was started due to the Nemesis statue passing by Earth in 1913. (DW: Silver Nemesis). Some of the battlegrounds were Passchendaele, the Somme and Gallipoli (DW: The Sea Devils, TW: To the Last Man). A million British soldiers died during the war. (TW: To the Last Man). The time-traveling Family of Blood, while in 1913, had warned some people there would be a war the next year. (DW: The Family of Blood)
In 1915, the RMS Lusitania was sunk, precipitating the United States getting involved. (BFA: The Sirens of Time)
The immortal Jack Harkness fought in the war (DW: Utopia), as did Tim Latimer (DW: The Family of Blood). Tommy Brockless also served, and was eventually executed in 1918, when, suffering from shell shock, he refused to return to the front lines (TW: To the Last Man). Solomon and the older members of his Hooverville fought in "the Great War," (DW: Evolution of the Daleks), as did Diagoras (DW: Daleks in Manhattan)
Several soldiers were kidnapped by the War Lords for use in their War Games. (DW: The War Games)
The Doctor visited the war several times. The Doctor along with Susan survived a Zeppelin air raid. (DW: Planet of Giants). In 1914, the Doctor, Tobias Philby and Thomas ended up in a no man's land in France, where they learned of a German artillery build-up and warned the British Army of it. (TVC: The Amateur) The Doctor also claimed to have been wounded at Gallipoli. (DW: The Sea Devils)