Here is the standard UNSC fleet organization, hope you like it. Updated as of May 28th, 2015.
Task Element: 1 vessel; EX: UNSC Canberra (CG-070); Fleet Officer: Captain, Commander, or Lieutenant Commander
Task Unit or Flotilla: 6 littoral combat ships, 7 frigates, 3 destroyers; EX: 81st Escort Flotilla, Task Force Dakota; Fleet Officer: Commodore Admiral
Squadron: 4-12 destroyers; EX: Destroyer Squadron 60, 3rd Fleet; Fleet Officer: Commodore Admiral
Division: 3-16 vessels; EX: Line Division 05, Battlegroup Mount, 1st "Home" Fleet; Fleet Officer: Rear Admiral (LH)
Battlegroup: 8 littoral combat ships, 10 frigates, 4-10 destroyers, 1-7 cruisers, 1-3 carriers, 2 assault ships, and 1-2 dreadnoughts or battlecruisers (possible); EX: Battlegroup Helios 14th Fleet; Fleet Officer: Rear Admiral (UH) or Vice Admiral
Carrier Strike Group: 8 littoral combat ships, 10 frigates, 7 destroyers, 9 cruisers, 2 assault ships, 2 carriers, and 1 supercarrier (possible); EX: CSG 79, 3rd Fleet; Fleet Officer: Rear Admiral (UH) or Vice Admiral
Task Force: 8-65 littoral combat ships, 80 frigates, 56 destroyers, 1-32 cruisers, 1-12 battlecruisers, 1-10 battleships, 1-4 dreadnoughts (possible), 40 assault ships, 19-40 carriers, 1 supercarrier (possible); EX: Sol Aegis, 1st "Home" Fleet; Fleet Officer: Vice Admiral or Admiral (Full)
Sector Fleet: 13-78 littoral combat ships, 150 frigates, 100 destroyers, 1-25 cruisers, 1-22 battlecruisers, 1-18 battleships, 2-8 dreadnoughts, 1-4 supercarriers; EX: 5th Fleet; Fleet Officer: Fleet Admiral
I took some of it off the internet. By the 2540s and 2550s, the UNSC Navy had at least 20 fleets that are active. I decided to change a few things to it. I am going to the Marine Corps next. Strident-class vessels are the first littoral combat ships in service with UNSC, being used as fast attack vessels and fleet escorts, the Infinity-class battle carrier is capable of holding ten of these in her sub-vessel hangers. Littoral combat ships are frigate-sized warships capable of speeding through embattled space faster than standard frigates, they have taken the place of all corvettes in the UNSC fleet.