Very interested in how this works, for those who were educated and wanted to become Officers, did the draft/conscription force these trainee-Officers to stop their training and enter the War as lowly ranked privates?
What about medical students finishing their studies, when they were drafted, were they drafted into regular infantry, or were given the Officer training route to become Military doctors with a better pay and rank?
Procurement of officers in the pre-war and wartime U.S. Army used several methods;
Regular Army officers already serving.
National Guard officers called into federal service.
Graduated ROTC candidates. Those still taking their training were students and constituted a deferred class as they were not yet commissioned; they were commissioned into the Enlisted Reserve Corps upon graduation.
Graduates of Officer Candidate Schools in the ground or air arms, established after July 1941. By definition, these men were already sworn into the Army and as enlisted men needed between four (for replacement men) and six months (for warrant officers and other enlisted men) of service to apply for admission, provided that they had achieved the requisite AGCT score (110) and had passed the medical examinations necessary for their selected branch of service.
Graduates of the Army Specialized Training Program, an ROTC-like curriculum at colleges that produced enlisted men and warrant officers trained in technical specialties that had the option of accepting officer commissions if they chose. Due to the sufficient number of personnel obtained from other sources and the ASTP's small number of graduates at a time, the program was drastically cut back in February 1944 with most personnel being sent to combat arms.
Civilians who had completed four successive one-month phases in the Citizens' Military Training Camps between 1921 and 1940. The officer output of this scheme was rather disappointing, with only 5,000 men being commissioned into the Enlisted Reserve Corps in the 20 years of the program.
Civilians in skilled occupations sworn in as enlisted men or commissioned as officers, serving in positions such as in the Medical Department, Ordnance Department, or Signal Corps. It was intended that these men receive the same courses in military discipline as any others, but the pressures of mobilization often drastically reduced the amount of training.
Under this scheme a telephone corporation was asked to furnish officer and enlisted personnel for an entire signal construction company, and an automobile manufacturer was called on to produce an ordnance maintenance company.
There was a large surplus of trained officers in the U.S. Army prior to World War II due to the establishment of an Organized Reserve of 27 divisions immediately after World War I, and the situation regarding immediate mobilization and shortages of troops was much better in 1940 than it was in 1917.
I made a rather lengthy post about the mechanical aspects of the draft here and I will reproduce it below;