Actually, there were Army Black Americans driving in the DUKW’s and one earned a medal for valor for risking his life saving some wounded Marines whose boat flipped in the surf
And, I am sure there were black sailors
BRAVE AMERICANS ALL
13. “Seeking to rescue a Marine who was drowning in the surf at Iwo Jima, this sextet of Negro soldiers narrowly missed death themselves when their amphibian truck was swamped by heavy seas. From left to right, back row, they are T/5 L. C. Carter, Jr., Private John Bonner, Jr., Staff Sergeant Charles R. Johnson. Standing, from left to right, are T/5 A. B. Randle, T/5 Homer H. Gaines, and Private Willie Tellie.” March 11, 1945. S/Sgt. W. H. Feen. 127-N-114329 (african_americans_wwii_013.jpg)
102. “Iwo Jima...Negro Marines on the beach at Iwo Jima are, from left to right, Pfcs. Willie J. Kanody, Elif Hill, and John Alexander.” March 1945. C. Jones. 127-N-11383. (african_americans_wwii_102.jpg)
110. “Carrying a Jap[anese] prisoner from stockade to be evacuated and treated for malnutrition. Iwo Jima.” February 23, 1945. Don Fox. 127-N-110622. (african_americans_wwii_110.jpg)
http://www.archives.gov/research/african-americans/ww2-pictures/#army