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The historical origins of the differentiation between `inertialÂ¿ and `noninertialÂ¿ quality gyroscopes is explained and the use of `noninertialÂ¿ gyroscopes in vehicle systems is utlined. This encompasses use for vehicle stability, directional references and controls, sight line stabilisation and crude inertial navigation and guidance. This latter use emphasises why the terms above have been put in inverted commas. The applications require the vehicle positional attitude or the vehicle angular rate. Until recently, these have always been obtained by using position (or free) gyros and rate gyros, respectively, but the advent of high-speed computing has made it possible for rate gyroscopes to perform both tasks (but not, generally, vice versa). This has made it possible, in some cases, to replace two gyro systems by one system, with obvious savings, but the one system must combine the requisite qualities of the two it replaces. The qualities required of gyroscopes for the applications listed above are outlined and some typical parameters are quoted. The difference between 'iron' gyros and optical gyros in terms of their performance is emphasised, especially the noise and drift-rate characteristics. The importance of these characteristics with relation to the applications is discussed.