The monograph which follows has been prepared for the Institute by Wing Commander E. W. Anderson and Mr. J. B. Parker, working closely with Mr. D. H. Sadler. It was designed primarily for publication in book form; however, the Council has decided to publish it in the Journal as well, so as to give it the best possible circulation among members. This arrangement has meant varying slightly the normal style of presentation in the Journal and apart from the title page and page numbers there is no difference between the published book and the pages which follow.

The standard formulae, assuming a spherical Earth, for converting distance on a rhumb-line track into differences of latitude and longitude are:

where C is the course and α is known as the middle latitude. It is approximately the mean latitude when both points are on the same side of the equator; tables of the correction to be applied to the mean latitude to give the middle latitude are given in most collections of nautical tables.

Inertia is that property of matter which opposes change of motion. Inertial navigation systems utilize this property for the detection and measurement of linear accelerations and rotations in order to arrive at velocity change and displacement relative to some known initial state in a particular frame of reference.

Of the 293 papers published in the Journal, eighty-two, or 28 per cent, have been concerned with astronomical navigation. This, however, gives a false impression of its present-day importance. There was a time when conventional astronomical navigation provided the only means of determining position, in the absence of recognizable landmarks; and it still provides the only fundamental method independent of man-controlled devices. But there has been no change in principle since accurate time became available through the combination of radio time-signals and chronometers. The papers have dealt with techniques only. The large number is evidence of the abiding interest in astronomical navigation; but it also indicates the realization that, while the principles of astronomical navigation are unchanged, the conditions of its application have undergone radical change. Techniques have had to be improved under the pressure of necessity, so that the practice of astronomical navigation is now simpler than it has ever been.

The problem of the determination of the observer's position on the Earth can be most easily solved in terms of the equatorial coordinates of the observer's zenith. From Fig. 1, in which the inner circle represents the Earth and the outer circle the celestial sphere, it can be seen that the zenithal point on the celestial sphere is its intersection with the prolongation of the radius to the observer's position. The geographical latitude of the observer is equal to the declination of the observer's zenith, and the geographical longitude is equal to the difference between Greenwich sidereal time (G.S.T.) and the right ascension of the observer's zenith. We can obtain G.S.T. by interpolation from a nautical almanac or directly from a separate watch or clock set to keep sidereal time.

The development of automatic dead reckoning navigation instruments owes its main impetus to the needs of the airman during the second world war. It was foreseen that manual plotting would not be adequate, for example, in bomber operations where frequent changes of course are desirable and speed and height are not always accurately maintained, and it was realized that automatic computing of position would provide improved reliability and accuracy. The instruments developed have been described elsewhere, and this paper outlines their early history rather than details of their design. It also indicates some future possibilities.

Existing instruments. The main instrumental aids to dead reckoning navigation which came into use during the 1939–45 war were the distant-reading gyro-magnetic compass, the air mileage unit and the air position indicator. From them evolved the ground position indicator and the wind finding attachment, both used for special purposes towards the end of the war.

Early in the 1930's Captain L. C. Bygrave constructed an experimental instrument which undoubtedly influenced later developments. This instrument was to be fed by a gyro-magnetic compass with heading and from an air log with air distance; on it could be set wind speed and direction and aircraft speed and course. The instrument showed departure in miles north-south and east-west.

Captain Giessler, who is now assistant to the director of the Auschuss für Funkortung (the German association concerned with radio navigation) was navigating officer of the Scharnhorst when that ship with the Gneisenau and Prinz Eugen broke through the English Channel in February 1942. It is thought that this account of the operation will interest many navigators, even though it is not entirely navigational in content.

Towards the end of 1941 the repairs to the battle-cruisers Schamhorst and Gneisenau, lying at Brest, and to the heavy cruiser Prinz Eugen were already so far advanced, in spite of continual very heavy air attacks, that a decision had to be made as to the further use of these forces.

IT has long been realized that the small fishing craft are inadequately supplied with modern navigational aids, and the reason why the most modern aid, radar, is not used is because its cost, weight and electrical power requirements are too great. In Great Britain a large number of small-boat fishermen, for instance in the herring drifter fleets, use Consol for offshore navigation, but this is not sufficiently accurate for navigating into harbour in bad visibility.

In 1951 the National Research Council of Canada undertook the development of a microwave course beacon as an aid to entering harbour. In 1953 the Ministry of Transport & Civil Aviation Group at the Admiralty Signal & Radar Establishment undertook the development of a similar beacon with a view to simplifying the shipborne equipment.

The beacon system is an adaptation of the old Lorenz type aircraft landing aid and consists of a microwave radio transmitter mounted at a harbour entrance and radiating in turn from each of two aerials which have beams overlapping in the horizontal plane. The transmitter is so sited that the line of intersection of the two beams lies along the safe course line for entering harbour. (Fig. 1 shows the orientation of the beams at the Scottish fishing port of Arbroath.)

For a number of years helicopter operations will mainly take place at operating altitudes between 500 and 2000 ft. Due to the inaccuracies of existing pressure altimeters vertical separation less than 1000 ft. cannot be applied and therefore maximum use will have to be made of lateral and longitudinal separation possibilities if the development of helicopter operations in high density areas is not to be impeded. As far as possible helicopter operations will be kept apart from fixed-wing traffic but this may be difficult to achieve in terminal areas where departing and arriving fixed-wing aircraft are at low altitude and the available airspace is restricted.

It is, therefore, essential that the navigational aid on which air traffic control base safe separation should be one which enables the helicopter pilot to adhere strictly to his pre-determined track and also provides him with an accurate measurement of progress along track. Quite apart from the air traffic control aspect, since the helicopter flies low, frequently in poor horizontal visibility and low cloud-base conditions, accurate track keeping is essential from the standpoint of avoiding obstructions or high ground in the vicinity of the route. Accurate and solid coverage over a wide area at low altitude is therefore an important requirement of any helicopter aid system, particularly in a high traffic density area such as western Europe.

Squadron Leader Bower gives some data regarding the accuracy of astronomical navigation in high-speed aircraft. No attempt was made to assess the absolute accuracy of astro-navigation, but the distance, when plotted on the chart, between pairs of sights taken on the same star was measured, with the following results.

The average spread between beam shots is consistently greater than that between fore and aft shots, and it is possible that acceleration errors, which can be sizable for high-speed aircraft, are responsible for this.

Errors Due To Aircraft Accelerations. Errors due to the combined effect of the aircraft's movement and the Earth's rotation give rise to errors in the position line.

The use of the Decca flight log is most simply illustrated by referring to an actual flight, in this case on a Viscount service out of London Airport.

Fig. 1, which is a section from the chart roll used on a recent service, shows the London Control Zone chart. Take-off was from runway 2 8 RIGHT on an IFR day and the outward bound clearance was Chertsey 2000 ft., Dunsfold 3000 ft. with a radar climb en route to Seaford. At the time when the pilots are fully occupied with after take-off drills, r.t. &c., and maximum concentration on instrument flying is necessary, a quick glance at the flight log is all that is necessary to check that the aircraft is on track. At this stage, in the event of radar failure, an accurate position of the aircraft can be passed to air traffic control at any time it is requested, and ‘flying well right of the centre line’ and subsequent resumption of track is easily effected.

Many of the major ports of the British Isles, including two of the most important, London and Liverpool, are situated at or near the head of sand-filled bays or estuaries. Their continued utility depends not only on the provision of adequate berthing facilities within the harbour area itself but also on the maintenance of a deep-water approach channel through the shoals of the outer estuary. In some cases the latter requisite is the more difficult of the two to achieve, especially where the bottom configuration is liable to considerable change over a relatively short period of time.

The problems connected with a changing sea-bed configuration come within the scope of loose-boundary hydraulics, a branch of flow mechanics which has only begun to be investigated. Some success in this direction has already been achieved using scale models of specific areas but many unsolved problems remain and much remains to be done.

Most readers of this Journal will know a good deal about the long-established practice of setting adrift in the sea sealed bottles or other watertight vessels containing messages or questionnaire papers. There are numerous records stretching over a very long term of years of this having been done with the aim of conveying information—often in a jovial sort of way, but sometimes when it was feared that a ship seemed likely to be lost. In the latter case to which very few authentic records relate, mariners fearing the worst adopted the practice for obvious enough reasons. In the former case, records of the practice are legion and, a century or so ago, it was a common thing for floating bottles with papers inside to be flung overboard from outbound emigrant ships. The habit was still fairly common in much more recent times, and the writer once had quite a goodly number of missives recovered from stranded beer and wine bottles which, after the conclusion of a farewell party, had been thrown out from ships bound for America from the Elbe and other departure points. Generally speaking, such corked bottles were used empty (apart from the enclosed message), and so would perform journeys decided in large part by the winds. Where a serious intent lay behind the launching of a bottle designed to convey true news of distress, no very strong hopes could ever have been reposed in the glass messenger, since there could never have been any idea as to when it might go ashore and be found. It is probable that many bottles carrying messages of the sort have, over the years, been broken on rocky coasts or have stranded on unvisited shores perhaps to suffer burial in shifting sands.

ON 24 October the second of the Institute's annual series of lectures for nautical school cadets was held, once more under the general title ‘Off the beaten track’, at the Royal Geographical Society's house. Over 550 cadets attended, from H.M.S. Conway, H.M.S. Worcester, the Nautical College Pangbourne, the School of Navigation, Southampton, King Edward VII Nautical School, the London Nautical School, the Reardon Smith Nautical College and the T.S. Arethusa. Members of the London Area Sea Cadet Corps and of the Westminster Sea Scouts also attended.

This paper gives a description in very general terms of where and at what seasons may be found the strong winds which occur in the upper atmosphere above 15,000 ft. and discusses briefly the clear air turbulence which is sometimes found in and near these strong winds.

Jet streams of temperate latitudes. Navigators are now well aware of the comparatively narrow bands of strong winds, known as jet streams, which occur in the upper troposphere in temperate latitudes. These jet streams, which can stretch for over 2000 miles on occasions, are very variable in position and in strength. It is probably true to say that there is a jet stream with wind speeds exceeding 60 kt. somewhere between Jan Mayen (N. 71°) and Gibraltar (N. 36°) every day, except in quiet summer weather and exceptionally on quiet days in other seasons. Fig. 1, from Durst and Davis shows a typical jet stream; these winds are associated with fronts though the fronts are often of the dry type with very little associated weather. For example, the strong northerly jet stream over the British Isles on 14 November 1949, with speeds of over 150 kt., occurred over a surface anticyclone; it was in this jet stream that the Comet I, on an early flight, experienced very severe turbulence. The level of the maximum wind in these jet streams is about 30,000 ft. though the exact height varies from case to case. Since they are so variable in position and strength the navigator must take particular note of them and a close liaison with the forecaster is clearly essential.

Dectra (Decca Track/Range) is one of two British systems recommended at the March 1954. meeting of Com. Division of I.C.A.O. in Montreal for evaluation by interested States. Arrangements are now being made to commence proving trials of Dectra at the end of this year or possibly the beginning of 1957. The trials will be made under the auspices of the Ministry of Supply and Ministry of Transport and Civil Aviation in this country and with the support of the Department of Transport in Newfoundland. The system is primarily designed for the navigation of fast jet aircraft across the North Atlantic, a problem intensified by air traffic control when more than 100 aircraft are in the air at the same time on those routes. It is, however, likely to prove valuable for other similar applications. The trials installation will cover the main route Prestwick–Gander.

We are told by Captain Greenvile Collins that Charles II was ‘A great lover of the noble art of navigation’. I think his brother, James, Duke of York, who became the Lord High Admiral at the happy Restoration in 1660, shared the same enthusiasm. Members of the Royal Society, including distinguished seamen, studied mathematics, mechanics and optics. The time was ripe for improvements to be tried out, under royal patronage, in ship design and construction as well as in the navigation of ships. English methods began to be regarded as not only the best but even as unnecessarily exacting, and we are told that Davis's backstaff was known as the English Quadrant by the French, and the English log and log-line for estimating a ship's speed through the water was better than the simpler methods popular with Spanish, Portuguese and Dutch mariners.

Before considering what animals can do, without conscious thought, in the way of navigation, it would be useful briefly to review their ability to pilot themselves, to find their way around an area in which they have already had experience. Here landmarks play an obviously vital role, and in many cases they are visual landmarks which we can appreciate ourselves. But often the characteristics of the environment to which the animal reacts are non-visual, detected by senses similar to ours but of much higher acuity. The sense of smell is of dominating importance among the mammals, which will go so far as to provide their own ‘scent flags’ along the boundaries of their private preserves. Sounds are often used to guide animals, particularly to another member of their species or to their prey. The bats have gone further and rely on a form of echo-location for guidance of their fast erratic flight through the darkness. They emit high-pitched, if not supersonic squeaks and detect and analyse the reflections back from obstacles even so slight as a piano-wire stretched across their path. Animal ‘sonar’ of this kind has also been demonstrated in a bird and probably is also to be found in fish and porpoises. Certain snakes are believed to detect their warm-blooded prey by special heat-receptors in the head. Many other examples could be cited and our knowledge of the means by which animals can determine their course in familiar territory is probably not yet exhaustive. We are only just beginning to appreciate and understand what they can do when they are in completely unfamiliar areas or when, known landmarks are present but cannot be used.