During operations, Nimitz-class carriers sail at the centre of a carrier battle group of ships that includes guided missile cruisers, destroyers, frigates, logistics ships and submarines.

BBC: News | In Depth | Military Fact Files

The US Navy has a carrier battle group in the Gulf - centred on the USS Carl Vinson - and a second, with the USS Enterprise , in the Arabian Sea.

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Since World War II up until 2008, we maintained the dominant military force in the Mediterranean, consisting of at least one carrier battle group and an amphibious Ready Group with an embarked Marine battalion, along with logistic support ships and other units.

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China will take longer still to gain the expertise needed to deploy a carrier-based battle group, with all its supporting vessels.

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