A full strength unit in a war-mobilized unit will have several hundred people. In the infantry, it is called a battlion - usually divided into companies; Administration Company, A (or Alpha) Company, B (or Bravo) Company, C (or Charlie) Company and D (or Delta) Company etc.
A battalion is commanded by a Lieutenant Colonel known as the Commanding Officer (CO), his Deputy Commanding Officer (DCO) is generally a major, and he also has an Adjutant to handle administrative matters, he is generally a captain. The senior enlisted man in the battalion is the Regimental Sergeant Major (RSM), ranked as a chief warrant officer. He is in charge of discipline for the battalion, handles prisoner collection, oversees the training of the senior NCOs and even the junior officers to an extent, and a bunch of other duties when in the field and in garrison. The Regimental Quartermaster Sergeant (RQMS) is ranked as a master warrant officer and handles the battalion‘s stores. All of these are lumped into Battalion Headquarters and/or Administration Company. Admin Coy will also contain pay clerks, storemen, drivers, vehicle and weapons technicians, the signalmen (?), medical personnel (including the Medical Officer (MO) etc.
The battalion can also be divided into Echelons - F echelon being the Fighting Echelon - the infantrymen of the rifle companies or AFVs of the armoured squadrons, with other echelons being located to the rear - in WW II this consisted of A and B Echelon, not sure if this has changed much or not - A Echelon contained the company/squadron HQs, CQMS, etc., and B Echelon was the deep rear with battalion HQ, supply train, etc.
Each infantry company is commanded by a Major and his position is called OC (Officer Commanding), with a captain as a second in command (2 i/c). The senior enlisted man in the company is the Company Sergeant Major (CSM), ranked as a Master Warrant Officer. He controls discipline and administration within the company. The Company Quartermaster Sergeant (CQMS) is ranked as a warrant officer and looks after company stores.
The company is divided further into platoons - in a rifle battalion, generally three platoons. The platoon is led by a Platoon Commander, ranked Lt or 2Lt, with a platoon second in command generally ranked as a warrant officer (sometimes also called the Platoon Warrant, or platoon 2 i/c).
Each platoon generally consists of three sections and a weapons detachment. The weapons det contains the support weapons of the platoon - 84mm Carl Gustav, C6 machine gun, 60mm mortar. Each section is led by a sergeant Section Commander with a master corporal 2 i/c - I believe the current configuration is 4 C7 rifles, 2 C7 rifles with M203 grenade launchers, and 2 C9 light machine guns. Stuff like grenades, M72 anti-armour weapons etc. are distributed as needed.
An armoured regiment is similarly set up, though their companies are called "squadrons".
This is all theoretical, and apologies if I‘ve gotten any of it wrong - I‘ve never served in a full strength, full time battalion and am sure someone can correct me if I‘ve mixed up my WW II knowledge with current practices. That should get you started, anyway. In general, companies and squadrons are between 100 and 200 men apiece, with battalions/regiments generally having 600-900 men in them.
Hope this helps.
