Hi Walter

Yes I suspect that the Manchester had three formation lights too. I have some documentation that shows that Formation lights were being experimented with in 1934, so not really a new idea at any point, but indeed the recipients of these lights were intended to be Heavy bombers and some Medium ones.

The problem still is one of finding a photo of the wing tip of a heavy bomber (up to about 1941) with three formation lights.

Cheers
James