During live-fire exercises dealing with air-to-air combat, remotely controlled drones are frequently used to simulate enemy aircraft. In modern times, the drones are fired on by planes loaded with some type of air-to-air missile, with the objective of the exercise being to destroy the drone. These test are usually done to ensure that guidance packages within the missiles will work, although they can be done to test other factors, such as a missile's susceptibility to jamming or to see if a new type of dodging technique will work against the missiles fired. Live-fire exercises involving air-to-surface work are usually centered around precision-guided munitions. In some cases, tests involving bombs will make use of derelict buildings or, even more frequently, vehicles. Live-fire bombing exercises are usually conducted with precision-guided munitions to ensure that they work correctly, but are also used to test new and experimental weapons to ensure that they work as they were originally designed to. These test are usually monitored by chase planes and by cameras to determine if everything worked as it was originally intended to. Live-fire exercises may also be conducted against planes for the purpose of testing a plane's susceptibility to SAM sites, or as a means to test a plane's stealth features. Naval live-fire exercises may use anti-ship missiles and torpedoes, although tests involving air-to-air and air-to-surface missile, guns and bombs are not uncommon. Navies conduct live-fire exercises to test elements of an integrated defense system, such as the US Aegis; namely, its ability to track and destroy enemy anti-ship missiles. Tests can also include an integrated defense system's compatibility to fire new missiles or newer versions of the same missile. Live-fire tests are also conducted with a CIWS system, which is designed as the last line of defense for a ship. Surface ships also frequently test-fire the various guns kept and maintained aboard the vessel; these can range from sidearms and rifles up to the 16" guns of the mothballed US s. This is done to maintain the skill and knowledge needed to operate the weapon. In the case of aircraft carriers, the pilots assigned to the carrier may conduct air-to-air and air-to-surface missile exercises similar to those of the air force; additionally, these pilots may also conduct live-fire exercises against derelict ships. Recent aircraft carriers have incorporated missile-launching systems, and have taken part in live-fire exercises involving missiles. For submarines, both fast attack and ballistic missile (or "boomers"), live-fire tests may include firing sea-to-land missiles at targets on shore or launching dummy ballistic missiles; however, the most frequent live-fire exercises conducted by submarines involve firing torpedoes at a target.