Thomas was a rifle company platoon sergeant with Third Platoon, E Company, 2nd Battalion, 28th Marines. On February 19, his unit landed with the first wave of Marines on the southern beach of Iwo Jima towards Mount Suribachi. On February 21, Thomas took over the command of the Third Platoon from his platoon commander who was wounded.
Thomas held a leadership position with Third Platoon, E Company, 2nd Battalion, 28th Marines. On February 19, he led the unit onto Iwo Jima's southern beach as part of the initial wave of Marines. Two days later, Thomas assumed command of Third Platoon after his commander was injured.