What is Combat stores ship?

Combat stores ships, or storeships, were originally a designation given to ships in the Age of Sail and immediately afterward that navies used to stow supplies and other goods for naval purposes. Today, the United States Navy and the Royal Navy operate modern combat store ships. The Sirius and Mars classes and the Fort Rosalie and Fort Victoria classes provide supplies, including frozen, chilled and dry provisions, and propulsion and aviation fuel to combatant ships that are at sea for extended periods of time. Storeships should not be confused with fast combat support ships or tenders.