The paper which follows was presented at an Ordinary Meeting of the Institute held in London on 26 January with the President, Rear-Admiral G. S. Ritchie, C.B., D.S.C, F.R.I.C.S. in the Chair.

In a survey of navigational aids which considers both the navigational problems and the means for their solution it is first worth looking back in history because the problems as well as the solutions have changed. It is difficult to decide at what point in time to start, though without any doubt the greatest changes have come in the past fifty years. Even the ancients had their problems; it appears that the Greek general, historian, and apparently sailor, Thucydides was disgraced and exiled in about 400 B.C. because he lost seven of his ships and failed to reach Thrace from Thasos in time to save it from the Spartans. His navigation may have been faulty and perhaps better navigational aids might have changed the course of history!