He worked near asbestos in the Navy and later died of mesothielioma.
His bio states he was in the Marines from 1947-50.
“While McQueen felt that asbestos used in movie soundstage insulation and race-drivers’ protective suits and helmets could have been involved, he believed his illness was a direct result of massive exposure while removing asbestos lagging from pipes aboard a troop ship during his time in the Marines.”
http://en.wikipedia.org/wiki/Steve_McQueen