The US 3rd Fleet was the third of the six fleets of the United States Navy, formed in 2219 shortly after the establishment of the United Earth Government. It were charged with protecting Mars and the important Babylon Stations and Shipyards orbiting the planet. From 2400 through the First War of Continuation, the fleet was commanded by Fleet Admiral Hector von Brown.
The fleet became famous after it participated in the First Battle of Mars, the first contact and combat with the Unity of the Core Worlds and it's navy. Despite suffering heavy casualties (upwards of fifty of the fleet's ~seventy-five warships), the fleet claimed a Pyrrhic victory and defeated a numerically superior Unity force.