Hello, Brian. My dad was in the 5th Marines (1st Div) during WWII. If your dad was on Iwo Jima, 6th Div was probably not the only outfit he served in. Iwo Jima was assaulted by elements of the 3rd, 4th, and 5th Divisions, reinforced. 6th Div hit Okinawa 1 Apr 45, along with 1st Div. (Some elements of 2nd Div were on the island later in the campaign.) I don't believe any part of the 6th was on Iwo Jima.