These charts are derived from the original tables of organization and equipment (T/O&Es) for each type of unit listed on the division chart. (The exact T/O&E is listed on the upper right hand corner of each chart) T/O&Es changed during the war -- sometimes, several times -- but we have derived the charts from the T/O&Es that were in effect during the 100th Infantry Division's combat service.
Sometimes, local commanders adapted the organization of their units to address combat exigencies.
An example of this was the formation, in some Seventh Army infantry regiments, of a regimental "G&G," or "Guard and Guide" Platoon, designed to fulfill some of the tactical requirements ofmilitary police, such as traffic control and prisoner of war escort and security missions. It is therefore possible that certain details of these organizational charts may not conform to exactly how each unit was organized at every moment during the 100th's action in the ETO . . . but this is how they were supposed to look, according to Army standards. The ranks listed are the ranks that were authorized to fill each billet. Of course, combat losses and other realities often caused positions to be underfilled, that is, manned by a soldier of lesser rank than was authorized by T/O&E. Positions marked by "Jr. EM" could be filled by a Private or PFC, and in the non-infantry positions, such as mechanic or medic, could often be filled by a Technician 5th, 4th, or 3d Grade as well.
MODERN SOLDIERS TAKE NOTE: Although certain elements of these organizational structures may seem familiar (and they should), remember that many details of these organizations were MARKEDLY different from modern units. The regimental supply officer (S-4) for example, was assigned to the Regimental Service Company, even though he served on regimental staff with the other staff officers assigned to the regimental headquarters company. These charts have been painstakingly derived from the appropriate primary source documents; do not let modern convention lead you astray!