From 1939, Netley Hospital was used for the treatment of military casualties and prisoners of war. This included numbers of soldiers returning from Dunkirk and even Rudolf Hess after his solo flight to Lanarkshire in 1941. Control of the hospital was handed to the US military in January of 1944, providing them with a medical facility on the southeast coast in preparation for the Allied invasion of Normandy. The army occupied a smaller building to the rear of the hospital complex, and the navy occupied the main building. The hospital had been constructed in 1856 to cope with the increasing number of casualties returning from the Crimean War. As such, the buildings were perceived as antiquated and inadequate by some of the American medical staff.

However, the hospital proved invaluable following D-Day with hundreds of men admitted each day with a reported 141 operations conducted in one 36-hour period. This mostly included men who had been sent to Omaha and Utah Beach. Significant preparations had been made including vast rows of beds and surgical instruments. Various accounts of the horrific injuries seen amongst returning casualties highlight the traumatic situations that medical staff faced, especially the nurses who provided ongoing care. Shell shock and gunshot wounds were prevalent, and many men suffered devastating injuries from exploding mines.

The hospital was transferred back into British hands in July of 1945 after an estimated 68,000 patients were treated in the previous 18 months. The hospital became increasingly obsolete after the war and during the 1960s suffered a large fire which damaged many of the buildings. Therefore, the site was eventually demolished in the 1970s, making way for the Royal Victoria Country Park. The park is still open today for visitors to see the site of the old hospital and visit the military cemetery which is located to the rear of the old hospital site.