This from my Haynes Manual RAF Battle of Britain Operations Manual explains some of the specific RAF radio issues and may be of interest:
"The key to effectively communicating with fighter squadrons in the air during the Battle of Britain clearly rested on a single route; radio. Or, to more accurately describe the system then in use, Wireless Telephony or W/T. However, the equipment being used during the summer of 1940 proved to be less than adequate for the task expected of it, with the W/T apparatus in use by RAF Fighter Command being the High Frequency (HF) T.R.9D set. In fact, it had been intended that by 1940 all fighter aircraft would have been converted to the Very High Frequency (VHF) T.R.1133 sets. (T.R. in both cases stood for Transmitter/Receiver)
In practice it was found that the range of the T.R.9D set was too short and its performance too variable to give efficient air-to-ground communication for Fighter Command’s interception system. Thus, experiments and arrangements were put in place as early as 1935 to develop a VHF set. At that time it was anticipated that the new VHF sets would be available ‘in five years’ time’. In other words, by sometime in 1940. Part of the problem with the HF sets, apart from range, was that the number of users of the high frequency band had increased dramatically (even in wartime) from when it had been adopted twelve years earlier. These users included civil, military and foreign stations and a real possibility existed that the sets might be jammed from stations two or three hundred miles away and for all of these reasons it was desirable that a replacement system should work in another frequency band. However, delays in development and production of a new VHF set persisted but eventually it appeared that eight sectors in No 11 and 12 Groups, involving up to 300 fighters, could be equipped with the new sets by September 1939 and by October service trials of the new T.R.1133 sets were being undertaken by Spitfires of 66 Squadron. The results were dramatic, and exceeded all expectations with an air-to-ground range of 140 miles and an air to air range of 100 miles. Speech was clearer, pilot’s controls simpler and quicker to operate, direction finding was sharper and in every way the T.R.1133 was beyond any comparison with the T.R.9D. Unfortunately, however, the first stage of the re-equipment plan did not work out as quickly as had been hoped although it was further planned that by May 1940 an improved version of the VHF set, the T.R.1143, would be coming into use although, at that stage, only partial re-equipment with the 1133 set had been achieved and the majority of aircraft still had the old H.F. T.R.9D sets. Production and supply of the 1133 or 1143 had failed the RAF at its very hour of greatest need. Further, the operation of a force equipped partly with one type of W.T. equipment and the other part of the force with the T.R.9D was unworkable. It was a dire situation for RAF Fighter Command to be facing on the very eve of battle, and it led to Air Chief Marshal Dowding to signal the Air Ministry and No 11,12 and 13 Groups:
‘In view of the necessity for maintaining flexibility in operation of all Fighter Squadrons at present time, and limited wireless apparatus available, all VHF equipment in aircraft is to be replaced by the HF T.R.9D sets forthwith.’
An angry Dowding then wrote to the Air Ministry on 1 June 1940 deploring the inadequacy of supplies which had forced him to abandon this the most successful form of fighter communication. Only by reverting to the old H.F. sets could anything like a workable R/T organisation be maintained and losing the advantages of the new VHF sets was a retrograde step and a bitter disappointment. This retrograde step certainly affected the operating efficiency of RAF Fighter Command during the Battle of Britain and there are many examples of poor R/T communications recorded in the operational narratives of squadrons during the Battle of Britain illustrating how unsatisfactory the High Frequency T.R.9D sets were. For example, over Chelmsford on 18 August 1940 only one section of a squadron came into action against a German formation. The other sections in the squadron failed to hear an order addressed by the squadron commander owing to loud interference by a German transmission in which conversation between enemy pilots could be plainly heard. There had also been similar experiences over Swanage on 15 August, for example. Sometimes, the T.R.9D sets worked well, but in general too much of the pilot’s time and attention was taken up in the sheer effort of passing and receiving messages, with interference a frequent distraction. As a case in point, one RAF Battle of Britain fighter pilot, Plt Off Ken McGlashan of 245 Sqn, was subsequently scathing of the ineffectual T.R.9D sets. Talking of his own experience over Dunkirk in May 1940 he said: ‘We still waged war with the primitive T.R.9D radio as well as doing battle with the enemy. Selecting a frequency could be likened to finding a TV channel through a sea of white hash and interference. And one had to constantly keep tuning and re-tuning if one was to have any hope at all of communicating or receiving information. Of course, in the midst of combat a pilot had limited free hands with which to attend to such a job but suddenly a screech came over the ineffectual radio and filled my helmet with an awful deafening, squawking cacophony of static. I learned later that it was another pilot trying to warn me of five Me 109s diving on us, but I was none the wiser. On this occasion, I was shot down. Later, in June 1940, whilst on patrol over Cherbourg I spotted three enemy aircraft climbing rapidly below us. I tried to warn our leader several times, as it was obvious he hadn’t yet seen them. Unfortunately, the T.R.9D was true to form yet again.’
The T.R.9D, however, remained the wireless set in operational use throughout the Battle of Britain but its failings were a desperate and daily worry for both fighter pilots and controllers alike. It would be impossible to say on how many occasions this ineffective piece of equipment led to the loss of pilots, the breakdown of air-to-air communications between pilots or the inability of controllers to pass intelligible information to their squadrons and the resulting failure to intercept raids.'
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