scanning for threats, tracking targets, and guiding missiles to interception. When they were designed, they had the most powerful electronic warfare equipment and the most advanced underwater surveillance system in the U.S. Navy. These ships were one of the first classes of warships to be built in modules, rather than being assembled from the bottom up. The greater size and equipment on the CG-47-class cruisers increased displacement from 6,900 tons of the DD-963-class destroyers to 9,600 tons of displacement for the heavier cruisers. Aegis cruisers can steam in any ocean and conduct multi-warfare operations anywhere. Some cruisers reported some structural problems in early service after extended periods in extremely heavy seas; they were generally corrected from the late 1980s to the mid-1990s. Several ships had superstructure cracks, which were repaired. These ships' superstructures were a modification of that on the Spruance-class destroyers and were required to support two deck-houses (one forward for antennas forward and starboard), and the aft deck-house housed the aft and port antenna arrays. The later Arleigh Burke-class Aegis destroyers are designed from the keel up to carry the SPY-1D radars and have them all clustered together on the forward deckhouse, saving space and weight and simplifying cooling requirements. The radar support equipment is closer together, minimizing cable runs and concentrating support equipment. Operations research was used to study manpower requirements for the Ticonderoga class. It was found that four officers and 44 enlisted sailors could be removed from the ship's complement by removing traditional posts that had been made obsolete. However, manpower savings achieved by eliminating the very manpower-intensive Mk 26 guided missile system and replacing it with the far more capable and versatile Mk 41 Vertical Launching System (VLS) were harder to emulate with the Mk 45 127 mm (5") gun systems. The Aegis Cruisers are "double-enders", and along with the Zumwalt class, are the only surface combatants in the fleet that employ two large-caliber guns. Vertical Launching System In addition to the added radar capability, the Ticonderoga-class ships built after USS Thomas S. Gates (CG-51) included two Mark 41 Vertical Launching Systems (VLS). The two VLS allow the ship to have 122 missile storage and launching tubes that can carry a wide variety of missiles, including Tomahawk cruise missiles, Standard Missile -2MR/ER and -6 surface-to-air missiles, Evolved SeaSparrow surface-to-air missiles, and RUM-139 anti-submarine warfare (ASW) ASROCs. More importantly, the VLS enables all missiles to