In *The Thin Red Line*, James Jones, an infantry combat veteran, describes American infantry platoons as having four squads. Did Mr. Jones become confused after the war, or was there a time when US infantry platoons had four squads?

Yes, but during a brief and relatively mundane period when only WWII is considered.

I covered the evolution of the U.S. Army infantry squad and platoon from World War I to the end of World War II in posts here and here and but since this applies to World War II, I’ll copy the latter post below. The rifle company saw a significant shakeup in November 1920 with the scrapping of the World War I "distinct-section" system and the adoption of identical eight-man squads to the platoon. There was one Browning Automatic Rifle authorized for each squad, and a second one was authorized provisionally in 1930. This arrangement remained basically unperturbed until 1938.

Per T/O&E (before 1943, each unit had a unique table of organization, T/O, and drew from a standardized table of basic allowances, T/BA, for equipment; in August 1943, the T/BA was scrapped and T/O&Es were reissued) 7-17 of December 6, 1938, the U.S. rifle squad was organized as follows. It had peacetime and wartime establishments, due in no small part to the interwar parsimony of Congress;

December 6, 1938 (peacetime):

r: armed with rifle, U.S., cal. .30, M1903

Equipment	Quantity
Rifle, U.S., cal. .30, M1903	7

December 6, 1938 (wartime):

r: armed with rifle, U.S., cal. .30, M1903

Equipment	Quantity
Rifle, U.S., cal. .30, M1903	11

When the new M1 Garand semi-automatic rifle began to appear in 1938, there were not enough available; one Browning Automatic Rifle and one pistol were authorized in the squad in place of one M1903 rifle.

Per T/O&E 7-17 of February 1, 1940, the U.S. rifle squad was organized as follows;

February 1, 1940:

r: armed with rifle, U.S., cal. .30, M1

Equipment	Quantity
Rifle, U.S., cal. .30, M1	12

On paper, all men were to be armed with the M1 Garand, although this often still was not the case. The Mk. IV grenade laucher, a U.S. copy of the World War I-era French VB, was declared obsolete in 1931, leaving the infantry squad without any man-portable antitank weapons until the introduction of the bazooka in 1942. Several decidedly dead-end methods were tried in the interwar period to remedy this.

You will also notice the absence of the Browning Automatic Rifle. Based on the February 1940 T/O&E, each platoon had four squads, three rifle and one "automatic weapons" squad of a sergeant, corporal, and two three-man BAR teams. The automatic weapons squad was deleted with the October 1, 1940 revision of T/O&E 7-17, although the BAR was not officially returned to the rifle squad yet; the organization of the rifle squad was otherwise unchanged from the previous T/O&E.

October 1, 1940:

r: armed with rifle, U.S., cal. .30, M1

Equipment	Quantity
Rifle, U.S., cal. .30, M1	12

On March 1, 1943, the BAR was "officially" returned to the rifle squad. The M1 grenade launcher for use with the M1903 Springfield rifle had been standardized on September 9, 1941. A suitable grenade launcher for the M1 Garand, the M7, was still in development, so the M1903 rifle was kept in the squad to provide a grenade-launching capability. Production of the M1 grenade launcher ended in May 1943, and it was declared limited standard on December 21, 1944.

The M7 grenade launcher was approved for standardization on February 11, 1943, and began production in May. The production proceeded extremely slowly at first and as a result, it would not begin to reach frontline troops in significant numbers until early 1944. The M1 Grenade Projection Adapter was proposed for standardization in the same Ordnance Committee item, and this motion was approved exactly one month later. This one-time-use device, a set of fins with a short shaft and three "claws," allowed a standard Mk II fragmentation grenade to be fired from an M1 rifle, and it almost completely superseded the older M17 fragmentation rifle grenade by the fall of 1944.

March 1, 1943:

Quantity	SSN	Rank	Role
1r	745	Sergeant	Squad leader
1gs	745	Corporal	Squad leader, assistant
7r	745	Pvt./Pfc.	Rifleman
1b	746	Pvt./Pfc.	Rifleman, automatic
1r	746	Pvt./Pfc.	Rifleman, automatic, assistant
1r	746	Pvt./Pfc.	Ammunition bearer

b: armed with rifle, automatic, cal. .30

g: armed with launcher, grenade, M1

r: armed with rifle, U.S., cal. .30, M1

s: armed with rifle, U.S., cal. .30, M1903A3

Equipment	Quantity
Launcher, grenade, M1	1
Rifle, Browning, automatic, cal. .30, M1918A2	1
Rifle, U.S., cal. .30, M1	11
Rifle, U.S., cal. 30, M1903A3	1

With the February 26, 1944 revision of T/O&E 7-17, squad leaders and their assistants were promoted to staff sergeant and sergeant, respectively. The M7 grenade launcher was beginning to enter widespread use, and was issued three to each rifle squad. In practice, the BAR, as it was not a true light machine gun, was often used as a one-man weapon. Many users removed the bipod and used it as a kind of battle rifle.

February 26, 1944:

Quantity	SSN	Rank	Role
1r	745	Staff Sergeant	Squad leader
1gr	745	Sergeant	Squad leader, assistant
7r(2gr)	745	Pvt./Pfc.	Rifleman
1b	746	Pvt./Pfc.	Rifleman, automatic
1r	746	Pvt./Pfc.	Rifleman, automatic, assistant
1r	746	Pvt./Pfc.	Ammunition bearer

b: armed with rifle, automatic, cal. .30

g: armed with launcher, grenade, M7

r: armed with rifle, U.S., cal. .30, M1

Equipment	Quantity
Launcher, grenade, M7	3
Rifle, Browning, automatic, cal. .30, M1918A2	1
Rifle, U.S., cal. .30, M1	11

Change 1 to T/O&E 7-15 (infantry battalion) of June 30, 1944 adjusted the composition of the battalion and some of its component units slightly:

The number of privates first class in the battalion headquarters company was reduced from 55 to 52, and the number of privates from 21 to 19, with a corresponding reduction in the number of M1 rifles issued.

Six M1919 light machine guns and two M3 submachine guns were issued unallocated to the battalion headquarters company as spare weapons or as augmentation to be given to component units.

Six BARs and six M3 submachine guns were issued unallocated to each rifle company headquarters, to be distributed as the company commander saw fit.

The number of privates first class in the heavy weapons company was reduced from 79 to 76, and the number of privates was reduced from 31 to 28, with a corresponding reduction in the number of M1 rifles issued.

Sources:

CORG Memorandum CORG-M-194 Organization and Equipment of the Infantry Rifle Squad: From Valley Forge to ROAD, by Virgil Ney.

U.S. Infantry Weapons of World War II, by Bruce N. Canfield

U.S. rifle grenades

T/O&E 7-15 Infantry Battalion, dated 26 February 1944

T/O&E 7-17 Infantry Rifle Company, dated 1 February 1940

T/O&E 7-17 Infantry Rifle Company, dated 1 October 1940

T/O&E 7-17 Infantry Rifle Company, dated 1 March 1943

T/O&E 7-17 Infantry Rifle Company, dated 26 February 1944