Until the past few years inertia navigation has been a little known subject due to a cloak of security; but recently a number of informative reports and articles have been published, notably those by Adams, Schnerb, and Klass, all published during 1956. Moreover, many of the components of inertial systems have emerged from the early development stage, during which they were largely monitored by military agencies, and may now be purchased with a guaranteed performance specification.