The Navy is used for force projection and supporting amphibious operations such as landings by the Marine Corps. Air support is also delivered from aircraft carriers; the US Navy also has a strong tradition in submarine warfare.
They also deploy at least one supercarrier, the USS George H.W. Bush, which is destroyed during the eighth week of war.
The USS Florida appears in both EndWar novels. It is a Virginia Class Submarine marked as SSN-805. This would mean that the Virginia Class was extended because the Navy currently has 30 planned. The Florida would be the 32nd ship of the class in the fifth block (assuming no additional classes were built).
The USS Reagan Seabase appears to be one of the mobile sea bases spoken of in the mission briefings.