Lapahie was recruited to become part of the Navajo Code Talking program at Camp Pendleton at Oceanside, California. An estimated 400 Navajos agents were trained to use the code and around 300 saw action in the field. Speaking Navajo and using an additional code within that, they were able to convey information and orders among Marine units and Navy warships and aircraft. The Code Talkers served in all six Marine divisions, Marine Raider battalions and Marine parachute units.
After the war Lapahie continued his education at the Coyne Electrical and Radio, Television School in Chicago. He graduated there and found a job in Witchita with Boeing as an Assembler. He later moved to Los Angeles and got a degree as Radio Operator. Later Lapahie found a job at the Los Angeles Airport with North American as an Aircraft Mechanic. He stayed with North American for 33 years, working on the Stratofortress Bomber, Minute Man Missile, Gemini and Apollo Space Program, and Space Shuttle Program. Harrison Lapahie died in Los Angeles on 26th November, 1985.