He later campaigned for civil rights and desegregation in Milwaukee, which resulted in the 1966 firebombing of his flooring business by the Grand Dragon of the Illinois Ku Klux Klan.
After training as a tank gunner he shipped to England and took part in the second wave of the Normandy D-Day invasion, arriving at Utah Beach on June 10, 1944 with the 9th Infantry Division.
During the invasion of Germany, Gilman destroyed a German tank single-handed, for which he was awarded the Distinguished Service Cross.
Gilman was accused of being a member of the National Committee to Secure Justice for the Rosenbergs and Morton Sobell, which he denied.
A month before the explosion Gilman reported that he had found a crushed baby mouse in an envelope placed into the mail slot of his home.