World War I:

In Europe, physicians and surgeons were separate and allowed recruitment of surgical consultants. But this was not the same in the U.S. Army when they prepped for war in 1916. There was no solution for recruitment of staff with specialized skills. To rectify this, leaders in American medicine formed a Physicians' Committee on Preparedness which passed a legislation, in 1916, that encouraged physicians to join the reserve corps. The 1916 legislation added a new reserve component which allowed medical corpsmen to become a colonel  in the reserves. Normal colonelcy took 20 years to receive. Colonel Mayo (Chair of the Physicians' Committee on Preparedness) was a physician and made colonel from this new legislation. As the head of the committee, Mayo created a system of assigning surgeons to deployed hospitals as well as maintaining the balance between the amount of civilian surgeons for the general population and military surgeons during wartime. During World War I, Europe had medical officers work with enlisted and nurses. Nurses were finally deployed forward in mobile hospitals and staged facilities despite their "civilian role" that was specifically recruited for by the Red Cross to be attached to the Army. All European countries followed the French medical strategy during the war: to reduce the time before point-of-wounding care initiated to deploy enlisted personnel from ambulance units to work with combatant units. This allowed more enlisted men than officers to be medically trained and be the first source of treatment as medics.

Also during the war, there was the temporary creation of medical department officers such as administrative and sanitation corps that focused on epidemiology and logistics. They were medical corps created of non-physicians with skills needed in areas that there were no physicians. These corps were remade for World War II and consolidated post World War II. 

Major General Merritte Ireland thought coordination and communication  was bad in World War I. He wanted to add more basic field medical knowledge to officers, so he established Medical Field Service School in 1921. This brought more skills to the medical corps and allowed experienced officers to practice command skills, control, and communication in pre-deployment situations. 

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Advancements made in World War I: 

1. Colonel Gilcrest's gas decontamination units

2. Colonel Lyster's aviation medical support units

3. Regular medical officers were in control of the medical systems and in operations in World War I

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World War II:

Military medical officers has a similar role in World War II as in World War I, where regular officers controlled and commanded. The reserve physicians were still the specialists and the majority of medical personnel had minimal military training of basic field skills to take care of themselves, not always effectively. Although the physicians had the military authority from their rank, they often applied authority in a medical setting because it was their domain where they knew what to do. 

Changes made from World War I was the increased numbers of officers assigned to support aviation arms and specialists in the AMEDD. More specialists in the AMEDD made graduate medical education which was at first a civilian program but turned into officer expertises. Yet, this was a problem because general practitioners were used for anything but now specialized officers could not do the job as effectively as general practitioners and vice versa. This continued to problems in the first military action of the Cold War: the Korean War.