WINDOW ROCK, Ariz. (AP) - Samuel Billison, a Navajo who as a Marine during World War II helped invent a secret code based on the tribal language to confound the Japanese, died Wednesday of a heart problem, according to the Navajo Nation.

Billison didn't have a birth certificate, but he was born on the floor of a hogan on the Navajo reservation in the mid-1920s. He was believed to be about 78.

Billison and other Navajo Marines, called the Code Talkers, used the code and their native language to communicate troop movements and orders, developing a secret vocabulary that renamed military armaments and equipment using rough equivalents in Navajo.

Airplanes became birds, ships became fish and weapons were named after various items. For example, the word "bomb" was replaced by the Navajo word for "egg." Amphibious units were designated "chal," or frogs.

Billison, in an interview with The Associated Press in 2001, said he joined the U.S. Marines right out of high school in 1943. He said he was sent to test as a Code Talker when he completed boot camp and the Marines realized he was fluent in Navajo and English.

"This code was very difficult to learn and a lot of the young Navajos didn't pass the tests," he said. "It was a code that was within the language. So a regular Navajo that didn't study that code had no idea what we were talking about even though it was their language."

Billison and his fellow Code Talkers were not allowed to discuss their work when they returned home after the war.

"When we were being discharged the Marines told us, 'If anybody asks you what you did with the Marines, just say you fought. Don't say anything about radio, about code or communication,"' Billison said.

The Defense Department first released information on the Code Talkers in 1968.

Billison traveled throughout the world to carry the story of the Code Talkers who "offered their language to allow the citizens of the United States the freedom that we are able to enjoy today," said Lawrence Morgan, speaker of the Navajo Nation Council.

Billison, who earned a doctorate from the University of New Mexico in Albuquerque, served on the Navajo Nation Council and the Navajo Area School Board Association, helped reorganize the education system under the Bureau of Indian Affairs, was a member of the former Kinlichee school board and had been Kinlichee chapter president, Morgan said.