An American infantry company operating under the "Series A" Tables of Organization and Equipment approved on January 14, 1918 (these tables were a slight tweak of the Series A tables that had been in use since August 8, 1917, just as American boots set foot on French soil) was organized as follows. Each platoon had a headquarters and four "sections" or squads, for a total of one officer and 58 men. Four platoons and a headquarters made up a company, that had a total of six officers and 250 men. The U.S. Army Center of Military History publication United States in the World War 1917-1919: Volume 1, Organization of the American Expeditionary Forces (PDF warning) has more information, including all of the post-January 14, 1918 Series A tables used by American forces.

Company Headquarters:

Men:

Quantity	Rank
1	Captain
1a	First Lieutenants
1p	First Sergeants
1r	Mess Sergeants
1r	Supply Sergeants
1gr	Corporals
4p	Cooks
4r	Mechanics
5k	Wagoners
2p	Buglers
4ir	Privates, 1st Class

Equipment:

Equipment	Quantity
Mules, draft	15kx
Carts, ration, 2 mule	1k
Carts, water, 1 mule	1k
Kitchens, rolling, 4 mule	1k
Wagons, combat, 4 mule	1k
Wagons, ration and baggage, 4 mule	1k
Bicycles	2
Grenade-dischargers, rifle	6e
Knives, trench	40d
Pistols	9
Rifles	19L

 

Four Platoons; in each platoon:

 

Platoon Headquarters:

Men:

Quantity	Rank
1b	First Lieutenants
1cpr	Sergeants
4sr	Privates

Equipment:

Equipment	Quantity
Pistols	2
Rifles	5

 

1st Section (Hand Bombers):^n

Men:

Quantity	Rank
2pr	Corporals
4 (1r, 3pr)	Privates, 1st Class
6r	Privates

Equipment:

Equipment	Quantity
Pistols	5
Rifles	12

 

2nd Section (Rifle Grenadiers):^o

Men:

Quantity	Rank
2pr	Corporals
1r	Privates, 1st Class
6r	Privates

Equipment:

Equipment	Quantity
Grenade-dischargers, rifle	6
Pistols	2
Rifles	9

 

3rd Section (Riflemen):

Men:

Quantity	Rank
1r	Sergeants
2r	Corporals
6r	Privates, 1st Class
8r	Privates

Equipment:

Equipment	Quantity
Rifles	17

 

4th Section (Automatic Riflemen):^mt

Men:

Quantity	Rank
1pr	Sergeants
2pr	Corporals
4fp	Privates, 1st Class
8r	Privates

Equipment:

Equipment	Quantity
Pistols	7
Rifles	11
Rifles, automatic	4t

 

Notes:

Note	Explanation
a	Senior first Lieutenant, second in command
b	1st and 4th Platoons commanded by first Lieutenants, 2nd and 3rd Platoons commanded by second Lieutenants. Additional officers in Regular Army from Reserve Corps or National Army
c	Assistant to platoon commander
d	To be distributed as needed
e	For replacement
f	Automatic-rifle gunners
g	Company clerk
i	Company agents and signalmen
k	From supply company, not included in total
L	Includes 8 rifles for automatic gunners not acting as such
m	4 automatic rifle teams, each consisting of 1 gunner and 2 carriers; 1 Corporal for each 2 guns
n	3 bomber squads, each consisting of; 1 leader, 1 thrower, 1 carrier, and 1 scout (3 pistols for throwers)
o	6 rifle grenadiers and 3 carriers
p	Armed with pistols only
pr	Armed with pistol and rifle
r	Armed with rifle only
s	Runners
t	2 automatic rifles per platoon (8 per company) ordinarily held as a company reserve, in which case corresponding automatic rifle teams are used as riflemen
x	Animals not furnished until further orders