conning tower

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A raised, enclosed observation post in a submarine, often being a means of entrance to the interior.
• noun The armored pilothouse of a warship.

from The Century Dictionary.

• noun The low, dome-shaped, shot-proof pilot-house of a war-vessel, particularly an ironclad.

from the GNU version of the Collaborative International Dictionary of English.

• noun archaic The shot-proof pilot house of a war vessel.
• the raised structure rising above the deck of a submarine.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun nautical The armoured control tower of an early iron warship from which the ship was navigated in battle
• noun nautical A connecting structure between the bridge and pressure hull of a submarine; in larger, modern submarines it contains the captain's cabin and is known as the sail

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an armored pilothouse on a warship
• noun a raised bridge on a submarine; often used for entering and exiting