Sentence:  They include the Navy 's Atlantic Command at Norfolk , Virginia , which <WSD>is</WSD> in contact with the Polaris subs ; NATO headquarters in Europe ; Air Force forward headquarters in Europe and in the Pacific , which control tactical fighters on ships and land bases ; and SAC , which controls long-range bombers and Atlas missiles . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)