Strategic Phase, aircraft may be transferred to any region, while it takes ships or fleets several weeks to travel from region to region. There are also 14 key regions throughout the world which are vital strategic ports with repair facilities for ships. As not all ports have this capability, control of these key regions is crucial in order to maintain the fighting capabilities of one's fleet at sea with less turnaround time for ship repair when ships are damaged in combat. The invasion of a central naval port in itself however, does not guarantee the surrender of a naval power, and may require the entire surrounding region to be occupied before starting the invasion. Ships There are several types of warship available: battleships, battlecruisers, fleet aircraft carriers, light carriers, escort aircraft carriers, heavy cruisers, light cruisers, destroyers, and submarines. Materials cost and length of completion time varies with the battleships costing the most and thus taking the longest time to construct, with submarines being the cheapest and having the shortest turnaround time. Each power starts out with a certain number of ships of each type. More can be constructed, and existing types and new models can be upgraded and created when R&D in certain areas is developed. The game places emphasis on battleships while limiting the effectiveness of aircraft carriers, thus not reflecting the realities of World War II which saw the decline of the battleship and rise of the aircraft carrier as the dominant warship in naval warfare. Battleships however, may be sunk by either heavy gunfire from other vessels, or being bombed repeatedly by carrier and land based aircraft. The game also increases the effectiveness of submarines, enabling submarine fleets to dominate sea battles during the initial engagement. Ships are organized into fleets, which can comprise up to 16 ships. Up to three fleets can be deployed by each power in battle, with up to 96 total ships committed to a battle. Fleets begin deployed in a column of two ships abreast with the strongest ships as the vanguard and the weakest in the rear. The deployment of fleets may cause problems during combat when a fleet becomes stuck and individual ships are unable to maneuver to redeploy (for example, due to a land obstacle), causing fragmentation of a fleet. Another type of ship that can be constructed but not controlled is transports. These are used for transporting