device that renders a selected unit invulnerable to attacks for a short period of time. The Soviet 'tank rush' was a popular strategy online, involving building many heavy tanks and overwhelming the opponent with sheer numbers. The Allies' forces are generally cheaper, faster to build and more agile. Their infantry can survive longer with good use of their Medic unit. The Allies' strongest tank (the Medium Tank) is weaker in a one-on-one engagement against the Soviets' starting tank (the Heavy Tank), but it is also slightly faster and less expensive. The Allies also have anti-tank minelayers to counter superior Soviet armour. The Allies have only one air unit, the anti-tank AH-64 Apache attack helicopter (erroneously called 'Longbow' despite lacking the distinctive FCR of the same name), compared to three Soviet air units; however, the Allies also have anti-aircraft guns (more powerful but shorter-ranged than Soviet Surface to Air Missiles). Allied defenses against ground assaults — pillboxes and turret emplacements — are less powerful than the Soviets' Tesla Coil, but cheaper and better protected while also less dependent on electricity. On maps with water, Allies possess a major advantage in naval power thanks to the Destroyer, a versatile medium-sized warship armed with guided missiles capable of engaging all targets on land, sea and air, and the Cruiser (erroneously depicted as an Iowa-class battleship in cut-scenes), a large warship for shore bombardment equipped with turret-mounted 8-inch naval guns giving it the longest-ranged and most powerful surface-to-surface attack in the game. The Allies also possess several other tools of subterfuge and military intelligence, such as spies to gain information on or disable enemy facilities, and thieves for stealing enemy resources, hiding their own units and structures from detection via the 'gap generator' (a special tower outfitted with electronic warfare equipment, which creates a "fog of war" preventing enemy players from being able to see the tower or anything else in a large radius around itself), and revealing the whole game map with a prototype GPS satellite. The Allies' secret weapon is the Chronosphere, which temporarily teleports a selected unit to another part of the map. In online play and computer skirmish, both Allied and Soviet forces have access to the transport helicopters and the missile silo, which is not available to either side in single-player mode (though missile silos are found in some Soviet bases in the latter half of the Allied campaign).