. At Iwo Jima, Major Howard Connor, 5th Marine Division signal officer, had six Navajo code talkers working around the clock during the first two days of the battle. These six sent and received over 800 messages, all without error. Connor later stated, "Were it not for the Navajos, the Marines would never have taken Iwo Jima."
http://www.history.navy.mil/faqs/faq61-2.htm