Invisibility Rules the Waves

Stealth technology strives to keep military ships invisible to modern detection systems including radar, magnetic sensors, heat sensors, and acoustic detectors. There are many different types of stealth technology. For example, dazzle camouflage involves painting a ship with a camouflage pattern. Other methods help make ships inconspicuous by matching the brightness of the craft to its background via isoluminance, or using outward-facing bright lights. These techniques work best in open seas. In recent years, naval ships have been deployed to conflicts taking place in coastal waters, leading to the need for other stealth techniques.
If the enemy has radar, a camouflaged ship can be spotted. Soon after radar was invented, radar stealth technology began attempting to make ships invisible to radar. To avoid detection, ships must either absorb the emitted radio pulses, deflect the reflections away from the enemy's receiver, or cancel them by sending out radio waves that are out of phase with the actual radar echo. Achieving any of these is difficult owing to how radio pulses interact with ships. Vessels have both a radar cross section (RCS), a representation of its overall echo intensity, and a radar signature, or the waveform of a detected radar echo used to discriminate between targets. The RCS is determined by the size and shape of a ship and the angle at which the radar pulse hits. A smaller RCS allows a ship to be closer to the enemy without detection. Since most ships have a large RCS, designers try to reduce it by using decoys, firing bits of metal into the air to generate a larger RCS and a more attractive target to the enemy.
A ship's RCS can be reduced by decreasing its reflected energy by covering it with radar absorbent paints or foam. A ship can also be built of low radar reflectivity materials such as fiberglass, carbon (C)-fiber composites, and glass-reinforced plastic. Since a ship's sharp angles reflect energy back towards the receiver, reducing these also reduces detection.
Using a combination of techniques can make ships much more difficult to detect although never completely invisible.