Today, we're revisiting the topic of the ages of those who served in the U.S. armed forces during World War 2, because we have new information to add to it!

Before we go any further, the reason we're doing this is because this information plays a key part in one of the projects we're developing behind the scenes here at Political Calculations, which we'll be presenting in bits and seemingly unrelated pieces throughout this year.

So what information are we adding today? Well, it's about the end of volunteerism and the institutionalization of mandatory conscription for filling the ranks of the U.S. Army, Army Air Corps, Navy and Marines during the Second World War.

Air Force Magazine's John T. Correll explains more about how the American tradition of volunteering for military service came to be rejected by the executive order of President Franklin D. Roosevelt:

In 1936, an obscure Army major, Lewis B. Hershey, was appointed the executive officer of the Joint Army-Navy Selective Service Committee, set up to prepare for possible mobilization. The panel consisted of two officers and two clerks. Hershey was a former schoolteacher who joined the National Guard in 1911 and transferred to the regular Army after World War I. Nobody, least of all Hershey, dreamed the job would last for decades....

When Germany in 1940 invaded the Low Countries and France, Congress authorized the first peacetime draft in American history. Inductions began in November 1940. The following year, Hershey was promoted to brigadier general and named director of the Selective Service.

A total of 10.1 million men were drafted during World War II. At the beginning of the war, men rushed to enlist, but, from Hershey’s perspective, that ruined orderly conscription. He persuaded President Roosevelt in December 1942 to end voluntary enlistments except for men under 18 and over 38.

Prior to President Roosevelt issuing Executive Order 9279 on 5 December 1942, American men between the ages of 21 and 36 were subject to the military draft. In his executive order, in addition to eliminating volunteerism and fixed-term enlistments, President Roosevelt also took advantage of legislation passed by the U.S. Congress on 11 November 1942 to expand the eligible age range to be subject to the draft to include all men from the ages of 18 through 37. Volunteering for service was only permitted for those under the age of 18 and up to the age of 45 who claimed they could satisfy the military's enlistment requirements.

The birth years that coincide with these age ranges are shown in our updated chart below:

The end of volunteerism with the draft explains why the average age of those who served in World War 2 is 26 - it is the middle of the range from which the pool of those conscripted were drawn into service in the years from 5 December 1942 through the end of the war in 1945.

But more importantly, with how the draft worked during World War 2, by lottery, the age distribution of those conscripted into military service in a given year would be fairly even, rather than being heavily concentrated around a given age. The size of any bell-curve that might normally have formed was therefore minimized as a result of the policy.

That evenness of age distribution among those who served in the armed forces during World War II, in turn, explains a lot of things that turn up repeatedly in various datasets after the war. And that is something we'll be revisiting throughout the year....