The ethnic composition of the Army during World War II generally mirrored the ethnic composition of the country at the time with one notable exception, although certain aspects such as names, accents, and mannerisms might be played up if a director or writer needs to push along the plot using certain points. The Selective Training and Service Act, which was essentially the sole means of accession into the U.S. armed forces after the end of 1942, stated “That in the selection and training of men under this Act, and in the interpretation and execution of the provisions of this Act, there shall be no discrimination against any person on account of race or color.” The only visible statistical and representational exception among Army personnel is that of African Americans, who were rejected at higher rates for military service for various reasons, and once they entered the Army, with only one exception served in segregated units separate from white personnel.

In 1940, about 11.6 million people in the United States were foreign-born, or about one in every eleven; about 4 million were not yet naturalized citizens. 18.8% of people had at least one parent who was born outside the United States.

Race of U.S. Population, 1940 Census

Race	1940 census	%
All races	131,669,275	100.0%
White	118,214,870	89.78
Nonwhite	13,454,405	10.22
Of which
Negro	12,865,518	9.77
American Indian	333,969	0.25
Japanese	126,947	0.09
Chinese	77,504	0.058
Filipino	45,563	0.034
Hindu	2,405	0.001
Korean	1,711	0.001
Polynesian	657	0.0004
Other	131	0.00009

Race of Enlisted and Inducted Personnel, United States Army: From July 1, 1940 to June 30, 1945

Race	U.S. Army	%
All races	9,863,969	100.0%
White	8,790,538	89.12
Nonwhite	1,073,431	10.88
Of which
Negro	909,457	9.21
Puerto Rican	59,421	0.60
American Indian	22,676	0.23
Japanese	21,949	0.22
Chinese	13,499	0.14
Filipino	12,947	0.13
Hawaiian	2,367	0.02
Other	31,115	0.31

The racial categories in the 1940 census were "White," "Negro," "Indian" (Native American), "Chinese," "Japanese," "Filipino," "Hindu," and "Korean." If a person identified as any other race, it was to be entered in full. Hispanic Americans, barring the below exceptions, were to be regarded as "white." Persons of mixed white and African American ancestry were to be regarded as African American, while persons of mixed Native American and African American ancestry were to be regarded as African American. "A person of mixed white and Indian blood should be returned as an Indian, if enrolled on an Indian agency or reservation roll, or if not so enrolled, if the proportion of Indian blood is one-fourth or more, or if the person is regarded as an Indian in the community where he lives. Any mixture of white and nonwhite should be reported according to the nonwhite parent. Mixtures of nonwhite races should be reported according to the race of the father, except that Negro-Indian should be reported as Negro."

It was estimated that there were about 3 million Hispanic Americans in the United States, counted in the "white" category, of which about 90 percent could trace their ancestry to or had been born in Mexico.

The size of the “other” category in the second table could be explained, essentially, by the interesting precision of the Army in recording one’s race if they were not white or African American. In filling out the WD AGO Form 20, or “Soldier’s Qualification Card,” that followed an enlisted man throughout his service (the equivalent form for an officer was the WD AGO Form 66), interviewers were instructed to,

Indicate race by printing “W”...for enlisted men of white American or European stock. All other entries in this space will be recorded in full. If the man is a Negro or mulatto [mixed race], enter “Negro.” Distinguish between orientals by entering "Chinese," "Japanese," etc., as the case may be. A man whose parental stock is native to India will be distinguished by recording “Oriental Indian.” For an American aborigine record "American Indian." Examples of groups that will be distinguished are "Mexican," "Chilean," "Filipino," "Eskimo," "Arabian," etc. The Army is interested in individuals and in assigning them to training and duty where they will be of most value to the service and where they can make the greatest contribution to the war effort; otherwise it is not concerned with racial interpretation.

It as been estimated that about 500,000 Hispanic Americans served in the U.S. armed forces during World War II. More often than not, and seemingly, the vast majority of the time, they were recorded by the Army using the Census' definition of “white" rather than another group to be distinguished, such as "Mexican" or "Cuban" (unless, of course, they made it known they wanted to be identified as such), making tabulation of the exact number who served difficult.