Appendix A: The Skinner Report at Swanage (1940) Transcribed from the original in RSRE TRE 4/4/457 Preliminary Reports on Tests on Ships using 10cm Waves - November, December 1940 by H. W. B. Skinner The following tests were performed at Swanage by Members of TRE, and subsequently by Members of the Signal School, Portsmouth, who were temporarily attached here. The apparatus used was the GEC E.1198 Magnetron (9.1cm) as transmitter, and a crystal mixer with 4Smc IF. The transmitter power was nominally SkW, but the exact amount radiated is not exactly known. Transmitting and receiving aerials were placed at the foci of paraboloidal mirrors, 3ft in diameter, giving a gain of about 500. These were mounted so that their axes could be pointed towards the ship, manually or otherwise. In a few experiments, flat cylindrical-parabolic mirrors with an aperture of 6ft x 9in were used. The gain of these mirrors is about 250. We thought that the flat beam (narrow in a horizontal plane but about ±15° in a vertical plane) might be suitable for use on a ship, rolling in a rough sea. The alternative would be a complex system of gyro­ stabilization. Three sets of radio-apparatus were used - A and B, of which B was an almost exact copy of A. Apparatus C was also very similar, the main difference being that it was better engineered. The performances of the three sets of apparatus were not quite identical. This is unfortunately inevitable in the present early state of development of 10cm apparatus. TEST 1. 7th November, 1940. Apparatus A - Site Leeson House (250ft) Sea fairly calm. The Tit/ark, a boat of 92 tons and steel construction was foIlowed end-on to 7 nautical miles (signal approximately 3 times noise). The boat began to return towards the apparatus. Signals very clear, though fluctuating, the whole time. TEST 2. 11th November, 1940. Apparatus B - Site Leesoll House (250ft) Sea fairly calm. Submarine (U-class, the Usk) was seen up to about 7\12 nautical miles. Strong signals up to 6 nautical miles. These figures apply to the stern-on view. The broadside-on view seemed to give signals about twice as strong. Horizontal polarization of the source seemed slightly preferable to vertical polarization. Between 4 and 41;2 miles, the submarine dived and the signal disappeared. On coming to the surface, the signal re-appeared at a time when at most the periscope and conning-tower were visible. Signals at extreme range are always rather fluctuating, and at extreme range were liable to disappear for rather long intervals. 274 The Skinner Report at Swanage (1940) 275 TEST 3. 8th December, 1940. Apparatus C - Site Leeson House (250ft) Sea fairly smooth. Titlark followed end-on to 12 nautical miles (signal equal to noise). It seems probable that in the interval between Tests 1 and 3, some slight improvement in the apparatus had been effected. TEST 4. 15th December, 1940. Apparatus B - Site Leeson House (250ft) Sea fairly calm. Titlark followed end-on to 9 miles, but seen as strong echo at 10 miles when turning. From this it seems that Apparatus B was somewhat less sensitive than Apparatus C, but probably about the same as Apparatus A. TEST 5. 16th December, 1940. Apparatus B - Site Peveril Point (60ft) Sea calm. Titlark followed end-on to 5 nautical miles; seen turning at 6.3 miles. Signals otherwise similar to those in the previous tests. TEST 6. 17th December, 1940. Apparatus B - Site near Swanage Pier (20ft). Sea fairly calm. Titlark followed end-on 3.5 nautical miles. TEST 7. 18th December, 1940. Apparatus B - Site near Swanage Pier (20ft). Sea fairly calm. The flat paraboloids were substituted for the circular mirrors. The Titlark was followed end-on to about 3 nautical miles. The decrease in range is due to the lower gain of the flat parabolic mirrors. * * * It is characteristic of ship-detection that the signal strength decreases very rapidly with range near the extreme range. This is much more marked than for an aeroplane signal, as would be expected theoretically. For a ship we may have a very clear echo at a certain range, but at a range of Ih or 1 mile greater, the ship may be practically invisible. This applies especially to observations from low altitudes. This fact makes it doubtful if a considerable increase of range can be obtained by increased transmitter power. On the other hand somewhat increased ranges would probably be obtained by the use of wavelengths even shorter than 9cm. It would appear probable that the Usk gives somewhat weaker signals than the Titlark, though not very much weaker. The range obtained for the Titlark from different heights could very likely be reproduced for the Usk, with a maximum range difference of not more than about Ih mile. H. W. B. SKINNER TRE 4/4/457 20th December, 1940 HWBS/MT This is the report referred to in History jj, para.3S2, note (2). (See Chap.1, ref.4.) Appendix B: Radar in Convoy Protection (1942) The paper which follows dated 4 October 1942 gives a good idea of the situation prevailing at that date - just eighteen months after type 271 first went to sea for the Orchis trials - as well as quoting reports of some of the actions in which radar played a significant role. It was addressed to all 171 seagoing ships then in the Western Approaches Command - 57 destroyers, 23 sloops, 9 frigates, 9 coastguard cutters, 67 corvettes and 6 others, as well as many shore authorities. Drafted initially by Lieutenant A. ,. B. Naish, RNVR, Command RDF Officer, it was signed by the Commander-in-Chief, Admiral Sir Percy Noble. There is a copy in ADM 220/78. Annotations in square brackets by the present author. From ... THE COMMANDER-IN-CHIEF, WESTERN APPROACHES Date ... 4th October, 1942 No.W.A.689/506 RDF IN CONVOY PROTECfION POLICY When the capabilities of Asdics became known to the enemy, U-boats adopted the policy of surface attack by night. This policy was immediately successful, and it soon became apparent that a means of detecting U-boats on the surface at night was a vital necessity. 2. RDF was introduced into the Western Approaches solely for this purpose. 3. In view of the varied uses to which RDF is now put, it is perhaps useful to stress that the detection of U-boats at night is the factor on which RDF policy in this Command must be based. 4. While experiments were in progress to adapt the then existing sets for A/S use, Signal School, with remarkable speed, produced type 271. It was immediately recognised that this was the answer to the surface U-boat, and the RDF policy of obtaining the maximum information of U-boats at night became identified with the policy of fitting the maximum number of RDF sets type 271. 5. The structural limitations of fitting type 271, involving compensation for top weight and in certain cases the removal of the director, are well known, but it is significant that these losses are accepted most willingly by those who have had most experience with type 271 in action against U-boats. 6. When type 271 was first used at sea, large numbers of breakdowns occurred, and even those sets which were in working order were frequently operating below the maximum efficiency. The electrical and structural weaknesses responsible for many of the early breakdowns have now been corrected, but the most important factor in the increased reliability of type 271 has been the appointment of experienced RDF officers to escort groups. It is now clear that type 271 can be made to work at sea, but it is also clear that occasional breakdown will continue to occur. The presence in the escort group of an experienced RDF 276 Radar in Convoy Protection (1942) 277 officer, equipped with an adequate supply of spare components, is an essential part of the present RDF policy. 7. It has seemed necessary to stress the technical side of the group RDF officer's work, as there are so far very few ratings capable of dealing with RDF defects, and this places the maintenance of RDF equipment in a rather different category from the maintenance of the rest of the ship's armament. 8. While a glance at the classified shipping losses is sufficient to show that RDF policy must be based on the U-boat, air warning cannot be neglected. The problem here is rather different. While it is most desirable that every escort should be fitted with type 271 to produce the most effective A/S screen, it is not essential for every ship to be fitted for air warning, and the remarkable success of H/F D /F has led, in certain ships, to the replacement of the air warning set by H/F D/F. While unable to compete with type 271 in the matter of U-boat detection, the air warning sets (types 286, 290 and 291) are designed to combine air and surface warning and in ships not fitted with type 271 they give valuable information of surface vessels and U-boats at close range. Until type 242 interrogators are fitted to type 271 the air warning sets provide the only means of identifying friendly ships and aircraft by IFF, and of making use of the shore RDF beacons. [Radar beacons were set up ashore for navigational use principally for aircraft but responded to ships' 1.5m radar. Harvester with type 286M got a response from St John's, Newfoundland, out to the limit of the range scale, 60 miles, with a bearing accuracy of ±5°.