In WWII, how a soldier would become a tanker or another position in the military often depended upon his job in civilian life. At the reception center, the newly enlisted man was assigned a Specification Serial Number that most closely matched his noncombat job. For the fighting jobs, such as rifleman or tank commander, there was no civilian equivalent, and so these jobs were assigned as needed based upon the Tables of Organization and Equipment (TO&Es) The Secretary General of the Army used a special formula to assign these men their jobs. The formula counted out the SSNs and came up with a rate of assignment per 1,000 newly enlisted men; for example 21.3 would be cooks (SSN 060), 77.0 would be light truck drivers (SSN 345), and 177.5 would be riflemen (SSN 745). SSNs below 500 denoted jobs that had some parallel in civilian life.

Per the TM 12-427 Military Occupational Classification of Enlisted Personnel (12 July 1944), the SSN for a medium tank crewman was "2736 Medium Tank Crewman." There was no specific SSN for a gunner, commander or driver; they were all 2736s. Light tank crewmen had SSN 1736 "Light Tank Crewman".

Each tank battalion was made up of a headquarters and headquarters company, (TO&E 17-26, 18 November 1944) three medium tank companies (TO&E 17-27, 18 November 1944), a light tank company (TO&E 17-17, 18 November 1944), a service company (TO&E 17-29, 18 November 1944), and an attached medical detachment (TO&E 17-25, 18 November 1944) Total strength including the medical detachment was 720; 39 officers and 678 enlisted men; the battalion commander was a Lieutenant Colonel. The battalion had 53 M4 Shermans, 17 M5 Stuarts, 6 105 mm-armed M4 Shermans (one in the headquarters of each medium tank company, and three in an assault gun platoon in the battalion headquarters), and 3 mortar carrier halftracks.

Light tank battalions (uncommon; only three were formed, the 744th, 758th Colored, and 759th) had only three tank companies, and the 6 105 mm-armed Shermans were replaced with a platoon of M8 Howitzer Motor Carriages in the headquarters company.

The commander of each medium tank company was a Captain. He commanded three platoons, each of five tanks. The number 1 tank in each platoon was commanded by a First or Second Lieutenant. The platoon sergeant, a Staff Sergeant, had the number 4 tank. The number 2, 3, and 5 tanks were commanded by Sergeants. Gunners were Corporals. Drivers were either T/4s (company and platoon commander and platoon sergeant's tanks) or T/5s (all other tanks) The higher rank of the driver in relation to command tanks is actually something I have yet to determine a reason for. Loaders and bow gunners were Privates or Privates First Class.

The "5 M4s = 1 Panther" story is a myth stemming from US tank doctrine; single tanks were never sent out alone to confront an enemy; the smallest deployed unit was always the platoon.

From TO&E 17-27:

Medium tank platoon

Tank	Commander	Gunner	Driver	Bow Gunner	Cannoneer (loader)
1	1st or 2nd Lieutenant	Corporal	T/4	Private or Pfc	Private or Pfc
2	Sergeant	Corporal	T/5	Private or Pfc	Private or Pfc
3	Sergeant	Corporal	T/5	Private or Pfc	Private or Pfc
4	Staff Sergeant	Corporal	T/4	Private or Pfc	Private or Pfc
5	Sergeant	Corporal	T/5	Private or Pfc	Private or Pfc

The light tank company was very similar. The organization was essentially the same as the medium tank company, except the 105 mm howitzer tank was deleted. The company commander was again a Captain, with a First or Second Lieutenant in command of each platoon. The light tank commanders, who doubled as loaders since the M5 tank only had a crew of four, were Sergeants, with platoon sergeants again being Staff Sergeants. The only difference in rank comparing to the medium tank company was that the gunner was a junior enlisted man (Private or Private First Class)

From TO&E 17-17:

Light tank platoon

Tank	Commander/Cannoneer	Gunner	Driver	Bow Gunner
1	1st or 2nd Lieutenant	Private or Pfc	T/4	Private or Pfc
2	Sergeant	Private or Pfc	T/5	Private or Pfc
3	Sergeant	Private or Pfc	T/5	Private or Pfc
4	Staff Sergeant	Private or Pfc	T/4	Private or Pfc
5	Sergeant	Private or Pfc	T/5	Private or Pfc

Each of the light armored divisions had three tank battalions. With one exception they were all denoted with one or two-digit numbers.

Armored Division	Tank Battalions
1st	1st, 4th, 13th (converted from regimental structure in July 1944)
2nd	-- (regimental structure)
3rd	-- (regimental structure)
4th	8th, 35th, 37th
5th	10th, 34th, 81st
6th	15th, 68th, 69th
7th	17th, 31st, 40th
8th	18th, 36th, 80th
9th	2nd, 14th, 90th
10th	3rd, 11th, 24th
11th	22nd, 41st, 42nd
12th	23rd, 43rd, 714th*
13th	24th, 45th, 46th
14th	25th, 47th, 48th
16th	5th, 16th, 26th
20th	9th, 20th, 27th

Separate tank battalions were usually assigned to infantry divisions, some on a semi-permanent basis. Separate tank battalions for the most part were denoted by a three-digit number beginning with 7. There were three exceptions to this rule:

• The 70th Tank Battalion, the Army's sole prewar separate tank battalion,

• The 191st-194th Tank Battalions, formed from National Guard tank companies,

• *The 44th Tank Battalion, originally organic to the 12th Armored Division, was detached during their training in the USA and sent to the Pacific; the 714th Tank Battalion, a separate battalion, was used to fill the gap.

31 separate tank battalions were in Europe on January 1, 1945:

The 70th (also served in North Africa and Sicily as a light tank battalion; converted to medium tanks before fighting in Europe), 191st (previously served in Tunisia and Italy), 701st, 702nd, 707th, 709th, 712th, 735th, 736th, 737th, 738th MX, 739th MX, 740th, 741st, 743rd, 744th Light, 745th, 746th, 747th, 748th, 749th, 750th, 753rd (previously served in Italy), 756th (previously served in Tunisia and Sicily as a light tank battalion; converted to medium tanks and then also served in Italy), 759th Light, 761st (Colored), 771st, 774th, 778th, 781st, 784th (Colored), 786th, and 787th

6 were in Italy:

The 751st, 752nd, 755th, 757th, 758th Light (Colored), and 760th

13 were in the Pacific:

The 44th, 193rd, 706th, 710th, 711th, 713th Flamethrower, 716th, 754th, 762nd, 763rd, 766th, 767th, and 775th

And six were en route to Europe:

The 717th, 772nd, 777th, 782nd, 786th, and 787th

Sources:

US Tank and Tank Destroyer Battalions in the ETO 1944-1945, by Steven J. Zaloga

Steel Victory: The Heroic Story of America's Independent Tank Battalions at War in Europe, by Harry Yeide

ETO Order of Battle- DIVISIONS

US Army in World War II: Armor and Tank Types, by Richard Anderson

US Army Specification Serial Numbers

United States Army in World War II: The Army Ground Forces; The Procurement and Training of Ground Combat Troops, by Robert R. Palmer