From Gineipaedia, the Legend of Galactic Heroes wiki
The Free Planets Alliance space navy consists of several space fleets that formed the principle defense force for all the FPA territories and member planets. They are commanded by experience flag officers. A regular FPA fleet comprises of around 12,000 ships usually commanded by a Vice Admiral that are organized as a numbered fleet, which in turn are divided in at least two ships wings of 6,000 ships commanded by a Rear Admiral.The wings are organized in several squadrons of 500 ships lead by a commodore or senior captain.The FPA navy also organizes its forces into many independent squadron, commanded by a rear admiral, these squadrons conduct anti piracy patrols and sector defense.
Combine fleets are formed from numbered fleets to provide the forces necessary to effectively carried out a defense campaign or offensive expedition. An Admiral or Fleet Admiral will be appointed as theater commander for such a fleet and direct the overall force.