In August 1940 the War Office requested use of part of Crichton Royal Hospital for a Military Hospital to accommodate Officer Patients suffering from mental and nervous disorders. The Board of Directors agreed to the request, having earlier in the year allowed a section of Maxwell House to be temporarily used to accommodate troops stationed in Dumfries who were on the Sick Roll. Grierson House was selected and the first patients arrived in December 1940. Agreements were put in place with the War Office as to alterations to the building, maintenance charges, staffing and treatment, and Physician Superintendent, Dr P. K. McCowan was in charge with the rank of Lieut.-Colonel. Patient accommodation had to be altered elsewhere at the hospital to allow Grierson House to be vacated for its new use, with patients being distributed among other hospital buildings. The Military Hospital patients were able to take advantage of and contribute to the extensive recreational and social activities available at Crichton Royal including dances, concerts and sporting events. By 1943, 1,237 Officers had received treatment and by 1944 the Military Hospital was fully occupied and a request was made by the War Office for further accommodation. At the end of the War the Military Hospital was still in operation with 2,165 Officer Patients having received treatment since its opening. After a request from the Board of Directors for Grierson House to be relinquished, due to overcrowding in other parts of the hospital, the building was handed back for Crichton Royal Hospital use in November 1946, with the remaining Officer patients being transferred to Netley Military Hospital.
In keeping with the hospital's long history of producing a patient magazine, the Officer patients resident at the Military Hospital produced their own magazine, The Crichton Scoop.