Military career
Tyrrell served in the medical branches of both the British Army and the Royal Air Force. He had joined the Royal Army Medical Corps (RAMC) (Special Reserve) in 1912 and served in the First World War from its onset in 1914. in 1915 Tyrrell made the famous discovery that urinating on a cloth and putting it over your face, the natural ammonia in the urine would neutralise the poison gas, so he encouraged other soldiers to do the same saving the "B Company" so they could stand and defend the line. During the war he was Mentioned in Despatches six times, was awarded the Distinguished Service Order and Bar in 1918, as well as the Military Cross in 1914 and was also awarded the Belgian Croix de Guerre in 1918. His service in the war was varied, serving as the Regimental Medical Officer with the 2nd Lancashire Fusiliers from 1914 to 1915; O.C. No1 M.A.C., from 1915 to 1916; and Deputy Assistant Director of Medical Services for VIII Corps of the British Expeditionary Force in 1916. From 1917 to 1918 he was the Officer Commanding the 76th Field Ambulance and in 1918 became the Assistant Commandant and Officer Commanding of the RAMC School of Instructors. He was seconded as Principal Medical Officer (PMO) to Headquarters Royal Air Force (RAF) with the Army of Occupation from 1918 to 1919. He continued to pursue a military career after the war. He was PMO Z Expedition Somaliland from 1919 to 1920. In 1920 he transferred to the RAF. He was the Senior Medical Officer in Basrah from 1922 to 1923.
In 1922 the War Office Committee of Enquiry Into "Shell-shock" published its final report providing an overview of the British experience of shell shock during the First World War. Tyrrell was a key contributor of evidence. He gave evidence in his capacity as a medical expert but he also described his own experience of shell shock which he suffered as a consequence of being buried by a shell explosion during his service as a medical officer to the 2nd Battalion Lancashire Fusiliers (12th Brigade, 4th division) on the Western Front. Tyrrell stated that it was his belief that the major cause of shell shock could be ascribed to the repression of fear.
From 1923 to 1926 Tyrrell was PMO in Palestine and from 1927 to 1931 PMO in Cranwell. From 1932 to 1935 he was PMO in Iraq and Middle East and in 1935 moved to Inland Areas Training and Technical Training Command where he remained until 1944. He became an air commodore in 1935 and an air vice marshal in 1939. In 1939 he also became honorary surgeon to King George VI of the United Kingdom a position he held until 1943. He retired in 1944 and from 1945 to 1947 was the Director of Medical Services to the British Overseas Airways Corporation.
In 1942 Tyrrell was created a Commander of the Order of the British Empire and in 1944 was appointed to the rank of Knight Commander of the Order of the British Empire, for his service during the Second World War. In 1947 he became a Knight of the Order of St John. He was painted by Walter Stoneman on two occasions.
