Stealth Technology

But how does it work?

The way most airplane identification works is by constantly bombarding airspace with a RADAR signal. When a plane flies into the path of the RADAR, a signal bounces back to a sensor that determines size, and location of the plane.
Other methods focus on measuring acoustic (sound) disturbances, visual contact, and infrared (heat) signatures.
Stealth technologies work by reducing or eliminating these attempts to identify aircraft.
Panels on the F-117 are angled so that radar is scattered and no signal goes back to base.
The F-117 uses flat window panels and radar-absorbing treatments on the cockpit windows and on the windows housing the bomb laser-guidance systems that block radar waves from entering these areas.
Planes are also covered in a layer of composite materials, special coatings which absorbe, and so reduce, any other signature the plane might leave.

Reducing the IR (heat) signature of an aircraft is also needed to make an aircraft more stealthier. The F-117 engine exhaust is diffused with cool air after exiting the engine, and it is spread by vanes to exhaust through wide shallow apertures accross the entire inboard trailing edges of both wings. The B-2 engine intakes and exhausts are situated on the upper surface of the wing where they are shielded from ground based radars.

The latest aircraft with stealth technology are the F-22 Raptor, F-35 Joint Strike Fighter and the Eurofighter Typhoon.
All three are, or will be, able to cruise at supersonic speed without using the afterburner, which leads to a greathly reduced IR signature when cruising supersonically.

Stealth at sea??

No, this is not for James Bond, this is for the US Navy!
DD 21 Zumwalt class multimission destroyers will enter service in about 2010 to replace Oliver Hazard Perry class frigates and Spruance class destroyers. Unlike previous classes of destroyer, the DD 21's primary mission is in providing land attack support for ground forces. Therefore high degree of signature reduction is very important to improve survivability for this class. Reducing its visual, radar, infrared, acoustic and magnetic signatures are the most important design goal. The ship is also to carry out traditional destroyer missions of anti-air, anti-surface and anti-submarine warfare.

The ship design will also likely include radical composite construction materials, some radar absorbing materials and optimized hull shaping both above and below the waterline. Extensive attention will also be given to acoustic quieting and degaussing for both equipment and propulsion systems. The integrated power system (IPS) is expected to provide substantial quieting capability.
Integrated Power System (IPS) is the all-electric architecture for future ships, providing electric power to the total ship (propulsion and ship service) with an integrated plant so the propulsion and all services connected to an electric bus. IPS offers reduced costs of ownership, reduced construction costs, improved survivability and greater architectural flexibility. The provision of electric drive will eliminate the need for drive shaft and reduction gears and will bring benefits in signature reduction, an increase in available power for weapon systems and improvements in the quality of life for crew.

The DD-21 Zumwalt-class will be armed with 5-inch/62 extended range guided munitions and 155mm Howitzers, the ship will provide naval gunfire support up to 100 miles inland.
A land attack missile system will extend support between 100 and 200 miles. Tactical Tomahawk missiles will be able to reach targets from 200 to 1,600 nautical miles. DD 21 will have the most advanced undersea warfare combat systems ever installed on a surface combatant.
The ship's hangar will house attack helicopters as well as a system of unmanned aerial vehicles (UAV).

Another stealth boat is the Swedish "Visby Class corvette".

The Visby Class corvette is the first vessel in the world to have fully developed stealth technology, combined with high operational versatility. The outstanding stealth properties fundamentally change the ship's survivability and improve its mission effectiveness.
Visby is a flexible surface combatant, designed for a wide range of roles: anti-surface warfare (ASuW), anti-submarine warfare (ASW), mine countermeasures (MCM), patrol and much more.
The Visby is designed to minimize all signatures - optical and infrared signature, above water acoustic and hydroacoustic signature, underwater electrical potential and magnetic signature, pressure signature, radar cross section and actively emitted signals.
The MCM system consists of a combination of extremely low signatures, sensors and weapons, and very high shock resistance.
A powerful sonar system is used to detect, locate, classify and supply real-time target data to the weapons.

The hull is designed on stealth principles with large flat angled surfaces. Every feature that need not necessarily be located outside the hull has been built in or concealed under specially designed hatches. The gas turbine exhausts have been concealed in hidden outlets close to the water surface at the stern of the vessel.
The vessel is built of sandwich-construction carbon fibre reinforced plastic (CFRP). The material provides high strength and rigidity, low weight, good shock resistance, low radar signature and low magnetic signature.
The material dramatically reduces the structural weight (typically 50% of a conventional steel hull). This results in a higher payload carrying capability, higher speed or longer range.