FN USN

The designation "FN USN" typically refers to "Fireman, United States Navy," which is an enlisted engineering rate within the U.S. Navy rather than a specific unit. The Fireman rating has its origins in the early days of steam-powered naval vessels, where Firemen were responsible for maintaining boilers and propulsion systems. Over time, the role evolved to include a broad range of engineering and mechanical tasks aboard ships and submarines, supporting essential operations. Today, U.S. Navy Firemen receive training in various engineering disciplines and often progress into specialized ratings such as Machinist’s Mate or Electrician’s Mate, playing a crucial part in maintaining fleet readiness and operational capability.