Frank Griffiths was involved in the development of Blind Landings during the war, and describes much about the systems and how they were tested in his book "Angel Visits" which is worth a read. His other book "Winged Hours" describes his tour as an SOE pilot on 138 Sqn at Tempsford, including his mission where he was shot down and his subsequent escape along the evasion lines back to the UK.
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