Inertial navigation

Inertial navigation is a technique of navigation that does not depend on external references such as compasses, stars, gravity or GPS, but computes the present position by sensing the movement of the navigating platform from a precisely known starting point in space. The general approach is to use multiple gyroscopes as references for the axes of position, as well as for error correction, with strain gauges or other accelerometers to sense the motion.

The method is exceptionally important for precision-guided munitions, space vehicles, and military ships, submarines and aircraft, because it
 * Does not require external navigation infrastructure
 * Is resistant to electronic warfare

Enabling technologies
[{Gyroscope]]s, first used as non-magnetic compasses and as true vertical indicators in aviation, are the fundamental enabling technology. Inertial navigation greatly benefited when gyroscope technology moved beyond mechanical to ring laser techniques, which do not require moving parts and can be much smaller.

Naval applications
Gyrocompasses were precursors of full inertial navigation.

A first major implementation was the Ship Inertial Navigation System aboard the first U.S. ballistic missile submarines, which needed absolutely precise position information for accurate missile launching, but whose operational security depended on not exposing themselves for star sights, radio navigation, etc. While the submarine systems have continued to improve, and intertial navigation became common on surface warships, the U.S. Navy became concerned that it was developing multiple systems where one would do, and that much less expensive commercial-off-the-shelf components were available.