Theodore DeWitt Allan was born in McAllister, Oklahoma, on 7 October 1894, son of George E. and Elizabeth Bentley Allan. He attended Presque Isle High School in Presque Isle, Maine, and Tufts College Dental School, Boston, Massachusetts graduating from the latter school with the degree of Doctor of Dental Medicine in June 1918. He enlisted in the Medical Reserve Corps (Army) on 16 December 1917, during World War I, and a year later was honorably discharged. In March 1919 he accepted a commission as Lieutenant in the Army Officer Reserve Corps (Dental), and in 1924 was promoted to Captain. He resigned to accept a commission as Lieutenant (jg) in the US Navy on 23 March 1925, and subsequently advanced to the rank of Captain, to date from 20 June 1942.
Leaving his private practice in Gloucester, Massachusetts, upon his call to active duty in March 1925, he served for five months as Assistant Dental Officer at the Naval Training Station, Newport, Rhode Island. From August until December 1925 he attended a postgraduate course at the Naval Dental School, Washington, DC, after which he returned to Newport to serve for another six months as Assistant Dental Officer. In June 1926 he joined USS Raleigh in which he served as Dental Officer for two years. He next had a tour of duty at the US Naval Academy, Annapolis, Maryland, and after service from July 1931 until June 1933 with the First Brigade Marines at Port au Prince, Haiti, he returned to the Academy to be Dental Officer until May 1936.
Sea duty until February 1938 as Dental Officer of USS Henderson, a transport operating between the United States and China Stations, was followed by four months' instruction (Dental and Oral) at Columbia University, New York, New York, and a tour of duty at the Navy Dental Dispensary, later the Navy Yard, Washington, DC. That tour completed in October 1940, he was ordered to Mobile Base Hospital #1, being formed in New York and sailing for Guantanamo Bay, Cuba, via USS Henderson. Shortly prior to the outbreak of War, he assisted in fitting out Mobile Base Hospital #2 at New York and served with that unit at Pearl Harbor, TH, after the Japanese attack on the Fleet there on 7 December 1941.
He had a facsimile of, and was entitled to wear the Ribbon for the Navy Unit Commendation awarded the US Naval Mobile Hospital Number TWO as follows: "For extremely meritorious service in support of military operations during the Japanese attack on Pearl Harbor, TH, on December 7, 1941. Exerting every effort to rush to completion facilities for handling casualties, personnel of the US Naval Mobile Hospital Number TWO quickly prepared for any emergency after approximately twenty Japanese planes appeared over the area enroute to attack Pacific Fleet ships and shore installations. Fire-fighting and battle stations were manned; operating teams were organized in the one building immediately sandbagged and converted into a temporary operating suite; and ambulances and trucks with stretchers were dispatched promptly to the Navy Yard. As the heavy stream of casualties mounted, this gallant organization worked unceasingly day and night for the relief of the hundreds of injured and, by the courage, initiative and valiant devotion to duty displayed throughout this grueling period, upheld the highest traditions of the US Naval Service."
Between February and April 1942 he served at the Naval Medical Supply Depot, Brooklyn, New York, in connection with fitting out US Navy Mobile Base Hospitals 4, 5, 6, 7, and 8. That assignment completed, he remained in New York for four months duty in the Office of Naval Officer Procurement at 33 Pine Street. He was next ordered to the National Naval Medical Center, Bethesda, Maryland, where for eight months he was Executive Officer of the Dental School. Detached in April 1943, he returned to Brooklyn as Senior Dental Officer at the US Navy Receiving Station, and, in June 1944 was transferred to like duty throughout the remaining war period with the US Marine Corps at Camp Lejeune, North Carolina.
In October 1946 he reported to the Naval Air Station, Memphis Tennessee, where he was the Dental 0fficer and served additionally on the staff of Commander Naval Air Bases, SIXTH Naval Air Technical Training Center. In February 1950 he was transferred to similar duty at the Naval Air Station, Jacksonville, Florida, with additional duty on the staff of Commander Naval Air Bases, SIXTH Naval District.
Under orders of 16 March 1953, he then served as District Dental Officer, FIRST Naval District, with Headquarters at Boston, Massachusetts.
In addition to the Navy Unit Commendation Ribbon, Captain Allan had the World War I Victory Medal; Second Nicaraguan Campaign Medal; China Service Medal; American Defense Service Medal; Asiatic-Pacific Campaign Medal; American Campaign Medal; World War II Victory Medal; and the National Defense Service Medal.
Captain Allan was a member of the American Dental Association, the Masonic Order, and the Benevolent and Protective Order of Elks.