Here is the organization for the UNSC Marines! SEMPER FI! Updated as July 9th, 2015.
Standard:
Fireteam - 4 marines; Commanding Officer: Lance Corporal to Sergeant; Example: Fireteam Delta, 4th Squad, 1st Platoon [Alpha Company, 1st (Infantry) Battalion]
Squad - 12 marines; Commanding Officer: Staff Sergeant; Example: 2nd Squad, 4th Platoon, Bravo Company [5th Battalion]
Platoon - 24 - 48 marines; Commanding Officer: 2nd Lieutenant; Example: 3rd Platoon, Charlie Company, 2nd Battalion
Company - 164 marines; Commanding Officer: Captain; Example: Kilo Company, 1st Battalion, 7th Marine Regiment
Battalion - 640 marines; Commanding Officer: Major or Lieutenant Colonel; Example: 3rd Battalion, 81st Marine Regiment, 405th Marine Division
Regiment - 3,200 marines; Commanding Officer: Colonel; Example: 172nd Marine Regiment, 21st Marine Division, 9th Marine Expeditionary Force
Division - 20,000 marines; Commanding Officer: Major General; Example: 2nd Marine Division, 56th Marine Expeditionary Force, 5th Fleet Marine Force
Marine Expeditionary Force - 40,000 to 50,000 marines; Commanding Officer: Lieutenant General; Example: 4th Marine Expeditionary Force, 8th Fleet Marine Force
Fleet Marine Force - 120,000 to 200,000 marines; Commanding Officer: General; Example: 3rd Fleet Marine Force
ODST:
Fireteam - 5 ODSTs; Commanding Officer: Sergeant; Example: Alpha-Nine, Alpha Squad, 4th Platoon [Bravo Company, 7th Battalion]
Squad - 10 ODSTs; Commanding Officer: Staff Sergeant; Example: Bravo Squad, 1st Platoon, Charlie Company [12th Battalion, 98th Shock Troops Regiment]
Platoon - 40 ODSTs; Commanding Officer: 2nd Lieutenant; Example: 1st Platoon, 19th Battalion, 501st Shock Troops Regiment
Company - 160 ODSTs; Commanding Officer: Captain; Example: Delta Company, 7th Battalion, 34th Shock Troops Regiment
Battalion - 800 to 1,000 ODSTs; Commanding Officer: Lieutenant Colonel; Example: 22nd Battalion, 18th Shock Troops Regiment, 105th Shock Troops Division
Regiment - 3,200 to 4,400 ODSTs; Commanding Officer: Colonel; Example: 501st Shock Troops Regiment, 105th Shock Troops Division, 94th Marine Expeditionary Force
Division - 12,800 to 17,600 ODSTs; Commanding Officer: Major General; Example: 105th Shock Troops Division, 94th Marine Expeditionary Force, 3rd Fleet Marine Force
A/N: UNSC-MC Brigadier Generals serves as the Divisional Executive Officer and as a field officer, in the both the "Regular" Marines and the ODSTs. The ODSTs are made up of six active divisions and a dozen or more in reserve (which are based on their home colonies), making it one of SOCOM's largest formations. The Marines have undergone a transformation of sorts, receiving new and improved weapons and equipment, making it one of the most potent branches of the United Nations Space Command in this new era.