References:
FM 101-10: Organization, Technical and Logistical Data (1 August 1945), PDF pages 90- 92
The Organization of Ground Combat Troops (United States Army in World War II: The Army Ground Forces
Seek, Strike, and Destroy: U.S. Army Tank Destroyer Doctrine in World War II by Dr. Christopher R. Gabel
Nafziger: Organizational Summary American Infantry Division Infantry Regiment 1 October 1940 Table of Organization T/O 7-11
Nafziger: Organization, American Truck Drawn Medium Field Artillery Battalion (Triangular Division) 1 October 1940, Table of Organization 6-95
US Tank and Tank Destroyer Battalions in the ETO 1944-45 by Stephen J. Zaloga

Early Years – 1940-1941

On 16 August 1940, when US Army Anti-Aircraft Regiments were directed to practice anti-tank fire, most anti-tank guns in the US Army were concentrated in the following units:

Infantry Regiment Anti-Tank Companies (12 x 37mm AT Guns per Company)
Light & Medium Field Artillery Battalions (6 x 37mm AT Guns in each Battalion's Headquarters Battery)

Leading to a Field Artillery Regiment (2 Battalions) having 12 x 37mm Anti-Tank Guns, and a Square Infantry Division's Field Artillery Brigade (3 Battalions) having 36 x 37mm Anti-Tank Guns. There were also a few “specialist” units having 75mm Anti-Tank guns, but they were minor in scope.

By April-May 1941, the US Army decided to pull the 37mm anti-tank guns from the Field Artillery (an attempt to remove them from the Infantry having failed) and concentrate them into divisional Anti-Tank battalions, along with a small reserve of GHQ Anti-Tank Battalions.

The formation of these provisional Anti-Tank units would be from:

Divisional Anti-Tank Battalions → From Divisional Artillery
GHQ Anti-Tank Battalions → From Corps/GHQ Artillery Brigades

They were activated by a War Department letter dated 24 June 1941, in time to take part in the big maneuvers of 1941.

The Carolinas Maneuvers (September 1941)

GHQ Anti-Tank Group (Regiment) (1941)

1 x Scout Car Platoon for reconnaissance
1 x Anti Tank Battalion (37mm)
1 x Anti Tank Battalions (75mm)
1 x Aviation Company

The Anti-Tank Battalions were organized as such:

1 x Infantry Platoon
1 x Engineer Platoon
3 x Anti-Tank Companies

Tank Attacker (TA) Group (Regiment) (1941)

NOTE: Three of these (Tank Attacker-1 [TA-1], Tank Attacker-2 [TA-2] and Tank Attacker-3 [TA-3]) were created by First Army (BLUE) in the November 1941 Carolinas maneuvers.

The organization for TA-1 was:

1 x Scout Car Platoon for reconnaissance
1 x Anti Tank Battalion (Self Propelled; 75mm and 37mm on half-tracks) (93d Anti Tank Battalion)
1 x Anti Tank Battalion (37mm Towed)
1 x Infantry Battalion
1 x Engineer Company
1 x Field Artillery Regiment
1 x Tank Company
1 x Aviation Company

Initial Tank Destroyer Planning

On 18 August 1941, the Army's Planning Branch was calling for a 55-division army; with the following anti-tank units:

55 x Divisional Anti-Tank Battalions – 1 organic to each Division
55 x Corps/Army Anti-Tank Battalions (pool troops)
110 x GHQ Anti-Tank Battalions (pool troops)
220 x Tank Destroyer Battalions in Total

With about four Anti-Tank Battalions per Division, about 25% of all troop strength in the Army would have been manning anti-tank units.

On 7 October 1941, General Marshall approved the figure of four battalions per division as a planning estimate, with the activation of 63 battalions as an immediate goal. Also, the name of these battalions was changed to “Tank Destroyers”.

On 27 November 1941, the War Department ordered the activation of 53 Tank Destroyer Battalions under GHQ control.

A later Directive on 3 December 1941 removed all existing Anti-Tank Battalions from their units and redesignated them as “Tank Destroyer” units; with their new unit numbers being assigned as follows:

From Infantry – 600 Range
From Armored – 700 Range
From Artillery – 800 Range

Re-Namings were along the lines of:

1st Infantry Division Anti-Tank Battalion (Provisional) → 601st Tank Destroyer Battalion
2nd Infantry Division Anti-Tank Battalion (Provisional) → 602nd Tank Destroyer Battalion
93d Infantry Division Anti-Tank Battalion (Provisional) → 893d Tank Destroyer Battalion
101st New York National Guard Antitank Battalion (Provisional) → 801st Tank Destroyer Battalion
etc.

By 18 December 1941, the initial tables for Tank Destroyer units were issued:

Tank Destroyer Battalion (Light) (TO & E 18-15) (24 December 1941)

Battalion HQ (3 Officers)
HQ Company (2 x Armored Command Cars, 6 Officers, 158 Enlisted)
3 x Tank Destroyer Companies (Light) (12 x 37mm Towed AT Guns or Self-Propelled Guns each; 5 Officers, 159 Enlisted)
1 x Pioneer Company (5 Officers, 171 Enlisted)
Attached Medical Detachment (1 x Cross-Country Ambulance, 2 Officers , 22 Enlisted)

Total Equipment: 1 motorized air compressor, 2 armored command cars with armament, 36 x towed/Self-Propelled 37mm anti-tank guns, 83 x .30 cal LMGs, 83 x .50 cal HMGs, 1 cross country ambulance.

Tank Destroyer Battalion (Heavy) (TO & E 18-25) (24 December 1941)

Battalion HQ (6 Officers)
HQ Company
3 x Tank Destroyer Companies (Heavy) (6 x 37mm SPAA, 4 x 37mm SP-AT, 3 x 3-in SP-AT each)
1 x Reconnaissance Company (6 Officers, 132 Enlisted)
Attached Medical Detachment (1 x Cross-Country Ambulance, 2 Officers , 22 Enlisted)

Total Equipment: 35 Officers, 807 Enlisted Men. 32 armored command cars, 30 armored personnel cars, 6 armored reconnaissance cars, 18 x 37mm self-propelled anti-aircraft guns, 12 x 37mm self-propelled anti-tank guns, 24 x 3-inch self-propelled anti-tank guns, 15 x .30 cal LMGs, 36 .50 cal LMGs, 1 cross-country ambulance, 37 x solo motorcycles, 14 x 1-ton cargo trailers, 26 x ¼-ton trucks, 15 x 3/4-ton command trucks, 12 x 3/4-ton weapons carriers, 27 x 2½-ton cargo trucks, 2 x 4-ton wreckers.

The 53 Tank Destroyer Battalions created in December 1941 under these TO&Es broke down proportionately as:

26 x Towed (Light) Battalions
2 x Self-Propelled (Light) Battalions
25 x Self-Propelled (Heavy) Battalions

The Tank Destroyer Units that fought in Operation TORCH and North Africa did so under these TO&Es:

601st TD Battalion (November 1942) (37mm M6 GMC / 75mm M3 GMC)
701st TD Battalion (November 1942) (37mm M6 GMC / 75mm M3 GMC)
894th TD Battalion (January 1943)
776th TD Battalion (January 1943) (3-inch M10 GMC)
805th TD Battalion (January 1943) (3-inch M10 GMC)
813th TD Battalion (January 1943)
899th TD Battalion (January 1943) (equipped with 3-inch M10 GMC upon arrival in Casablanca)

Tank Destroyer Revisions 1942-1944

The number of Tank Destroyer Battalions was reduced to 144 in early 1943, then 106 by the end of 1943. Of these 106 battalions, 61 went to ETO, 10 to the PTO and 35 were left in the US and declared surplus and converted to tank, amphibian tractor, or field artillery battalions in December 1943 to May 1944.

[EARLY TANK DESTROYER ORGANIZATION + LIST OF TANK DESTROYER UNITS AND FATES TO BE DONE LATER]

The Final Organizations, 1944-1945

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