The Channel is the English Channel, the stretch of water which separates southern England from northern France.
Portsmouth is one of the Channel Ports, situated on the coast of Hampshire. For many centuries, it was one of the principal dockyards of the Royal Navy, alongside Chatham, Deptford, Plymouth, and Woolwich.
Spithead is an area of the Solent, the stretch of water between the Hampshire coast and the Isle of Wight. It is what is known as a roadstead (a place outside of a harbour where a ship is able to lie at anchor).