His military service began in 1898, when he enlisted with the 1st Colorado Infantry, USV, for the Spanish–American War as a first sergeant.

Lear was playing golf at the country club in Memphis, Tennessee, in civilian clothes on July 6, 1941, when a convoy of 80 U.S. Army trucks carrying men of the 110th Quartermaster Regiment, 35th Division rolled past.

The troops in the passing trucks subjected a group of women in shorts to a series of whistles and "lewd and obscene" catcalls.

There was a storm of public criticism of Lear's actions from people who felt that the soldiers had been harshly and collectively punished when many had done nothing wrong.

In these maneuvers, Lear judged the control and discipline of the 35th Division to be unsatisfactory and relieved Truman of his command.

[4] Lear continued in command of the Second Army until he was relieved by Lieutenant General Lloyd Fredendall in April 1943.

As such, he overhauled the replacement system, but the war against Germany ended before the full benefits of his reforms could be realized.