Sen applied for a commission in the
Royal Flying Corps in November 1916, but his application was rejected as he was under age. After a period working in a bank, He was ordered to report to the
No. 1 School of Military Aeronautics at
Reading from the same date. A month later, on 14 September, while taking part in an offensive patrol, Sen experienced engine failure and dropped behind the rest of his patrol. As he stated later in a deposition for the
War Office, "...in attempting to catch up [with the remainder of the patrol, I] was lost in a cloud. Coming out [I] was attacked by 4 enemy machines. Both [fuel] tanks [were] hit & [I] crashed outside
Menin. Unwounded." He was eventually repatriated to the UK on 14 December 1918. ==Postwar years==