Native American "code talkers" who used their indigenous languages to keep critical military secrets from World War II enemies are finally getting their due in Congress, decades after their heroism.

Twenty-four years ago France bestowed its highest civilian honor on American Indians who used their ancestral words as shields, forging an unbreakable code to communicate troops movements and enemy positions that the German and Japanese failed to crack.

On Wednesday, top US lawmakers will do the same, presenting the Congressional Gold Medal to some 250 Native American code talkers and their relatives.

"This is long overdue," Wallace Coffey, chairman of the Comanche Nation, told AFP this week.

With dozens of his compatriots, Coffey traveled to Washington from the central state of Oklahoma to receive the medal on behalf of World War II's 17 Comanche code talkers, known in their native tongue as "Numurekwa'etuu."

American Indians from 33 tribes will be honored, most of them posthumously. Edmond Harjo of the Seminole tribe is still alive and will participate in the ceremony.

France paid tribute in 1989, when Pierre Messmer, Charles de Gaulle's former prime minister, traveled to Oklahoma to make members of the Choctaw and Comanche tribes Knights of the National Order of Merit.

By sending radio messages in their dialects, these soldiers foiled interceptions of the enemy on the European and Pacific fronts.

Some 400 Navajo soldiers, the group with the largest participation in World Wars I and II, received Congressional Gold Medals in 2000, but those from other tribes had to wait until 2008 for Congress to allocate the same award, and their ceremony taking place Wednesday.

"The government has been very slow to recognize anything of importance for American Indians, and that's one of the real resentments in the American Indian community today," said Herman Viola, author of "Warriors in Uniform: The Legacy of American Indian Heroism."

'Pregnant bird' meant bomber

The idea of using North American native tongues as a war tool emerged in 1918 when a US officer on the French front grew frustrated by repeated German interceptions of World War I communications. Four of his soldiers were Comanches.

"They got these four Comanches to start using our language to communicate military messages," said Lanny Asepermy, historian for the Comanche Indian Veterans Association.

"And the Germans didn't understand what the heck they were saying."

The US Army reproduced the coding on a large scale a generation later. While some Native American dialects are written, much of the grammar, pronunciation and slang of their languages remained a mystery for the enemy.

None of their codes was broken.

Hundreds of American Indians were trained for transmissions. Sometimes their code reflected the simplicity of an agrarian or rural culture: "bird" could mean a plane, while a "pregnant bird" meant a bomber.

Navajos, Comanches, Hopis and Muscogees employed a system by which each letter of the Latin alphabet was an Indian word. In Navajo, the word "moasi" means "cat," and it would be used to represent the letter "c."

The entire endeavor was an irony, given that the US government spent much of the 19th century trying to eradicate Native American culture.

Most Indians were not deemed US citizens at the time of the First World War, and for many their citizenship was earned in exchange for their military service.

Irene Permansu Lane, 84, is one of the last three living wives of the Comanche "code talkers." On Wednesday, after decades of waiting, she will receive a medal in the name of her husband Melvin Permansu of the 4th Signal Company of the 4th Infantry Division. He died in 1963.

"It was a very great moment that finally this came about for them," she said.

"I was just overjoyed that they were eventually recognized for what they had done."

John Parker, 58, choked up as he recalled his code-talker father Simmons Parker, and how he and fellow Native American soldiers spoke little about their service.

Much of the project was sworn to secrecy, with some participants taking that secret to their graves.

"They didn't really go on about it, they kept it on the down side," Parker said, but "Dad couldn't have been more proud to serve the country the way he did."