"Evidence of the importance of Kapustin Yar (V-2 test site in Soviet Union) was obtained by Western intelligence through debriefing of returning German scientists and spy flights. The first such flight reportedly took place in mid-1953 using a high flying Canberra aircraft of the RAF. Numerous circumstantial reports suggest this flight took place, using either a Canberra B2 or a PR3, but the UK Government has never admitted such a flight took place nor have any of the supposed participants provided direct evidence" /1/
Here is some information about the airplane.
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