RAF Blind/Beam Approach Training flights

Does anyone have information on the RAF Beam/Blind Approach
Training flights?

When they were created, disbanded and what formation they
reported to?

I am after the ones attached to Bomber Command, the 1501
to 1521 and 1535 flights. The earlier flights were known as 1
through 7 or 8 flight and in October 1941 had 1500 added
to their designation number, so 1 became 1501 etc.

The ones I am missing are 1504, probably formed in early 1941,
as 4 becoming 1504 in October. 1505, similar story to 1504.
Also 1511, 1512, 1514 and 1517 probably formed late 1941,
and finally 1535.

The formations all appear in the detailed Bomber Command
OOB for 4 February 1943 in the official history, which covers
operational and training units. They are gone in the 1945 OOB.

Also information on the "Air Bomber Training" Flights which
appear to have existed during 1943, 1, 3, 4 and 5 group all
having one on 4 February 1943.

Geoffrey Sinclair
Remove the nb for email.