"Karley is an Amestrian State Military officer stationed at Fort Briggs under the command of Major General Armstrong. As a primary communications officer for the fort, he is frequently seen toting a large radio transmitter or wired communications pack on his back while in transit and is often put in charge of relaying information and orders to Briggs troops in combat. Karley is first seen participating in Captain Buccaneer's mission to rescue the lost search party inside the tunnel created by the Homunculus Sloth and later appears as the head of communications during Major General Armstrong's role in the capture of Central Command."

(Source: Full Metal Alchemist Wiki)