Mr. Collins, Senior Scientific Officer at A & AEE, describes the testing of a modern strike aircraft navigation system. A brief description of such systems together with an outline of a typical flight profile leads to a discussion of the problems of evaluation and the techniques adopted. The paper was read by Mr. T. O. Coldwell, also of A & AEE, at a meeting of the Institute in London on 18 May 1977 with the President in the Chair.