During the First World War, from 1916 to 1918 Trotter served as a corporal with the Royal Engineers corps of signals as a despatch rider.
[1] He recovered and returned to his studies of geology at Armstrong College, where he was taught by George Lebour, Franklin Sibly, David Woolacott and Leonard Hawkes.
Trotter soon began to work with Sydney Hollingworth on the glacial geology around Brampton.
Trotter worked for the survey for the rest of his career, and by the time he retired in 1963, he had reached the position of assistant director (England and Wales).
[6] Trotter received the Lyell Fund in 1938 for his geological researches on the glacial and post-glacial phenomena of the Eden Valley.