Submariners shun the surface - with good reason. On top of the water they are exposed and vulnerable; immersed, they are cloaked with invisibility. Rarely does a sub skipper take his boat above periscope depth while out of port, and he would not risk coming even that close to the surface if there were another way to receive orders by radio and to check his position from time to time. Submarines have found employment in conflicts ranging from India to the Falkland Islands. Throughout, in every operation, with every kind of submarine, the watchword would be secrecy. `The whole name of the game is stealth,' declares Captain Fred P. Gustavson, a former Sturgeon-class attack sub skipper. `submarines do not fight fair. If it turns into a fair fight, the submariner ought to withdraw and come back another time.