It is helpful at an exhibition to have a catalogue of the items on view. As this symposium is in effect a display of the operational aspects of marine radar, it may be of value in this paper to attempt to catalogue these aspects. They can be divided into two groups as follows:

A. The aspects that determine the effectiveness of marine radar (the siting of the scanner and the operating policy followed, for example). These we propose to call the OPERATIONAL FACTORS.

B. The benefits obtainable from marine radar (i.e. those aspects that may be said to measure its effectiveness—the time and worry saved, for example). For these we suggest the term OPERATIONAL YIELDS.

The quartz clock has made possible a notable improvement in the precision of timekeeping, with the additional advantage of providing a standard of frequency as well. This is perhaps putting the cart before the horse, for the quartz crystal oscillator was developed in the first instance as a precision standard of frequency; it was then adapted, by frequency subdivision and the use of a low frequency output for driving a phonic motor from which seconds impulses could be taken, to serve as a clock. It is primarily from its use as a standard of frequency that it is of navigational interest, for various radio aids to navigation, such as Gee, Loran, Consol and Decca depend upon accurately standardized frequencies. For the satisfactory checking of a frequency, comparison must be made with a standard whose accuracy is at least one degree higher than that of the frequency which has to be checked. Calibration laboratories, in turn, require to check their own standards. As the rotation of the Earth provides our fundamental unit of time, it follows that time, and therefore also frequency, must be determined from astronomical observations; hence it is necessarily the responsibility of the Royal Greenwich Observatory to provide both time and frequency with an accuracy sufficient for all practical requirements. The practical requirements have become more stringent in recent years, and that is why great efforts have been made to improve the precision of time determination and of timekeeping at the Observatory.

1. Introduction. A detailed paper describing the theory and calculation of equivalent head winds on air routes has been prepared by J. S. Sawyer and is being published as a Meteorological Report. The present paper is a simplified account which draws largely on Mr. Sawyer's paper.

When regular air services over a route are being planned, the wind at the chosen level of flight is an important factor. From the long term point of view, aircraft require to be designed so as to operate economically against adverse winds, if not on all occasions at least on all but a small percentage of occasions; for example, British Overseas Airways Corporation usually specify an 85% regularity of operation as a minimum. Similarly, for short term planning, wind information is necessary for the computations regarding the averages and extremes of fuel consumption, payload, time of flight, and so on. The aircraft operator consequently requires to know the frequency distribution of winds on any given route at any time of the year.

In all sciences, the experimenter is constantly seeking to improve both the accuracy of his observations and the speed with which they can be obtained. He wishes, further, to use the minimum of basic equipment, and to obtain the maximum simplicity in collecting his results. Unfortunately, these factors frequently act in opposite senses: an expensive apparatus, for example, may be required to collect accurate data quickly. In certain fields, it is even worth while deliberately to sacrifice accuracy in order to gain advantage both in speed and simplicity. Thus, in astronomical navigation, it may be possible to simplify sight reduction, to cut down on the bulk of tables carried in the air, and to reduce the time taken for observation and reduction of a sight. The penalty will be a loss in accuracy, but, provided this is not reduced beyond a certain level, it may well be worth while. A review of the requirements for air navigation, and an examination of the problems of position finding by the stars against these requirements may lead to some conclusions as to whether an advantage is to be obtained by simplifying the methods.

The special features of polar navigation are examined with a view to the design of tables for astronomical navigation in polar regions. The use of long intercepts and curved position lines is thoroughly investigated. It is shown that considerable economy of presentation can be achieved; as an example, a one-page table covering all bodies and both polar caps is given. Making the fullest use of polar astronomy, samples are given of permanent tables for the Sun and stars independent of the Air Almana.

The following critical review of tabular methods for astronomical polar navigation was written originally as a comment on a proposal to extend the Astronomical Navigation Tables (at present limited to latitudes between S. 79° and N. 79°) to the poles. Although it has been slightly amended, it has not been entirely recast and it therefore still retains some of the ‘thinking on paper’ of the original version. So far as is known the tables proposed are new, but there is clearly no great originality involved.

Jet streams are fast moving air streams which appear at times in the levels between 15,000 and 40,000 feet; they are located in the tropical air above the polar front. In this paper examples are given and certain occasions are noted on which they have seriously influenced air navigation.

Early in 1948 when a few charts of the 225 mb. level were drawn to show temperature variations over an air route it was noticed that a very strong stream of air was seen along the line where the tropopause appeared to cut that level. This stream seemed of very considerable length and little width.

The basic principles of the detection and location of objects by radar are now widely known, and the performance requirements of a marine radar equipment have already been covered by the British Ministry of Transport specification. This paper describes and analyses operational experience gained in fitting and in operating a number of equipments manufactured to this specification.

Astro-navigation cannot be regarded at present as one of the principal aids to air navigation. It suffers, by comparison with radio aids, in that it is slow in use and much more subject to interruption by bad weather. The average navigator needs at least 15 minutes to take and plot a two-star fix with present methods. This is quite a long time in the air, though not prohibitive with present-day aircraft, and in consequence astro-navigation is now used extensively only on long flights over sea or desert where radio aids are lacking.

The three principal tasks of the navigator on an aerial survey expedition are to get to the survey base, to recognize and define the area to be surveyed, and to fly across this area in parallel flight lines so as to photograph it adequately and economically. During the survey, the courses flown, height, speed and the time of day chosen are all influenced by the demands of the camera and of the photogrammetric machines which will produce the map from the air photographs. For this reason it is essential that the navigator, on whose competence during the survey the results will largely depend, should have a proper understanding of photogrammetry, photography and of the basic principles of ground survey. It is true that the crew will include a photographer and that the photogrammetric aspects of the operation will have been considered beforehand by those responsible for briefing the crew; nevertheless there are always unexpected problems which arise in the field and every aspect of the undertaking must be at the fingertips of the navigator who, in the final count, is responsible for the photographic coverage of the area.

In the second issue of the Journal a system of grid navigation was described. This system warrants serious consideration because of its application to polar navigation and because it offers a means of simplifying navigation in high-performance single-seater aircraft of long range. These aircraft are going to present extreme difficulties, particularly in naval aviation, where fixing facilities and pilotage are limited.

It is generally agreed that the increasing speed of modern aircraft, together with the availability of short-range radio and radar aids, necessitates a fresh approach to astronomical methods; less accuracy can be tolerated in the calculations but greater speed is essential. There are three stages after observation : the derivation of the position of the heavenly body observed, usually from the Air Almanac; the solution of the astronomical spherical triangle, usually by means of reduction tables ; and the resulting plotting of the position lines and fix.

Experience gained in equipping some 24 vessels, varying in size from 700 to 4000 tons, with radar may be of interest, and perhaps of help in avoiding some of the pitfalls that can occur.

The problem of finding sufficient space in a small ship so that one instrument does not interfere with another is never an easy one. For example, to fit radar to a vessel whose wheelhouse superstructure is not more than 10 ft. long may entail building a radar tower of considerable height if the proper distance between the scanner and the magnetic compass is to be maintained. The magnetic effect of the tower on the compass will then have to be considered, and it may be necessary to build it of a non-magnetic material. Also the effect of the radar, when working, on the D.F. loop arises; a distance of 12 ft. between them is here necessary.

Once the performance requirements of the Ministry of Transport Specification have been met, there remains to be considered the arrangement of the equipment to enable the ship's officers to take full advantage of the high performance for which the specification provides. These considerations can be classed in three main categories: the method of presenting information to the navigating officer, the convenience of the various controls, and the facilities provided to enable superficial maintenance to be undertaken.

The introduction of radio aids to navigation of the hyperbolic type, such as Decca, Gee and Loran, resulted in the need for special charts. These charts, which are usually of the scale and projection appropriate to the occasion, have overprinted on them red, green and purple lattice lines, representing the families of confocal hyperbolae drawn with respect to the Master and Slaves of the radio system. The production of these lattice charts was extensively developed during the war, both in Great Britain and the U.S.A. To provide the mariner with satisfactory marine charts for use with the English Decca Chain, the Hydrographer of the Navy has latticed all the principal coastal charts of England and Wales, and the Danish Hydrographer has similarly latticed the Danish coastal charts.

Hitherto it has been the practice to compute the altitude and azimuth of a celestial body either for a D.R. position or a chosen position in the vicinity of the D.R. position and to compare the computed altitude with the observed altitude, the difference (the intercept) being marked off along a line drawn in the direction of the computed azimuth from the position used for computing, either ‘from’ or ‘towards’ the object; a perpendicular drawn at the end of the intercept is the position line of Marcq. St. Hilaire.

Prior to the outbreak of war in 1939, flight planning procedure was not generally practised in civil aviation operations except in a few outstanding cases. Such operations as the Imperial Airways transatlantic flying boat flights called for the careful compilation of a flight plan in order that an indication of the flight time could be obtained. Since the range of these boats did not provide for any very great reserve, the flight plan was obviously an essential part of the preparation for the flight. In the case of a few shorter range operations, flight planning was also carried out to a certain extent: one operator, for instance, adopted a procedure whereby departures and arrivals were made to a schedule, and the aircraft operated so as to comply with this schedule. The increase in the length of route stages and the need for more technical operation of aircraft from the economic point of view indicated the need for more general use of serious flight planning, and it is now well established that flight planning is essential to the safe and efficient operation of flights of all kinds.

The method described provides glide-paths for climbing and descending aircraft by combining in a single instrument information from the barometric altimeter and radar distance measuring equipment. Preliminary flight tests have shown that the method provides a smooth path along which an aircraft can be flown within close limits, and is one that appears sufficiently promising to justify further development.

Height separation has for years been a fundamental concept in the control of air traffic. It is the basic method of preventing collision during en-route navigation and in some holding procedures. The main reason for this is that a suitable instrument already exists in the form of the barometric altimeter, aninstrument which is intrinsically more accurate and reliable than any of the usual navigational aids.

The method proposed consists in measuring by means of a specially designed sextant the altitude and azimuth of a star simultaneously and using these two quantities with the declination to solve the astronomical spherical triangle. In this way, both the latitude and, by means of certain simple additions and subtractions in terms of the local hour angle which is found directly, the longitude are determined.

This paper describes a number of proposals concerning the correction of the errors of magnetic compasses. The first proposal concerns the correction, by means of special soft iron correctors, of the deviating effects of both vertically and horizontally induced magnetization.

A scheme for removing constant error without having to use algebraic addition or even having to record the existing deviations is next described.

A scheme is then suggested whereby, provided no constant deviation is present, a compass may be corrected for the effects of permanent magnetism in four operations, each of which consists of the complete removal of deviation on a particular heading by a particular corrector.

Possibilities of putting compasses below decks without seriously affecting their performance are also discussed; these particular suggestions cannot apply to merchant ships in which magnetic cargo is being transported. Suggestions are also made of correcting the compass by modifying the disposition of the magnetic material in the bridge structure instead of by adding a corrector to the compass binnacle.

Finally, a scheme is introduced to maintain an aeroplane compass mounting parallel to the surface of the Earth during a level turn by using the centrifugal force due to the turn.

This paper puts forward five separate suggestions concerned with the correction and siting of magnetic compasses. The suggestions are unrelated to each other except in the fact that they have all resulted from viewing the problems from a deliberately unconventional standpoint. Some of the solutions proposed may be of interest to those concerned with magnetic compasses in ships, aircraft and vehicles.

The flagship of the General Steam Navigation Company, s.s. Seamew (Captain T. C. Stone), 1209 tons, has recently completed various trips on which data relating to the use of her navigational radar have been noted. The data collected bear on many problems of presentation and practice and are described in this paper.