Please answer a question about the following article about Charleston, South Carolina:

During this period, the Weapons Station was the Atlantic Fleet's loadout base for all nuclear ballistic missile submarines. Two SSBN "Boomer" squadrons and a submarine tender were homeported at the Weapons Station, while one SSN attack squadron, Submarine Squadron 4, and a submarine tender were homeported at the Naval Base. At the 1996 closure of the station's Polaris Missile Facility Atlantic (POMFLANT), over 2,500 nuclear warheads and their UGM-27 Polaris, UGM-73 Poseidon, and UGM-96 Trident I delivery missiles (SLBM) were stored and maintained, guarded by a U.S. Marine Corps security force company.

Submarine Squadron 4 is homeported at what type of military base?
Naval Base