On the old board (http://www.rafcommands.com/cgi-bin/dcforum/dcboard.cgi?az=show_thread&om=10527&forum=DCForumI D6&archive=yes) I said as follows:

"I am trying to solve a mystery which is now 64 years old. My Uncle Bill was killed in action on the morning of 20 May 1944 over Le Mans, Sarthe, France, while bombing the railway marshalling yards. He was Bomb Aimer for the Deputy Master Bomber, and the family oral tradition had it that he was "shot down". Recent information from http://www.raf.mod.uk/bombercommand/may44.html has a different story:
'Le Mans: 112 Lancasters and 4 Mosquitos of Nos 3 and 8 Groups. The majority of the bombs hit the railway yards and caused serious damage. The local report says that the locomotive sheds were destroyed, an ammunition train (or some ammunition wagons) blew up, 2 main lines were destroyed and all other lines blocked because overhead power lines were brought down across the tracks. Unfortunately the Lancasters of the Master Bomber and his deputy collided over the target and crashed. The Master Bomber was a brilliant young New Zealander, Wing Commander JF Barron, DSO and Bar, DFC, DFM, and the Deputy Master Bomber was Squadron Leader JM Dennis, DSO, DFC They were both killed; both were from No 7 Squadron. 1 other Lancaster was lost.'

Does anyone have any idea where the details of the alleged collision might be documented? One of my correspondents has suggested that it might be considered unlikely for the Master Bomber and his Deputy to be in the same piece of airspace at the same time, and that they would have orbited on opposite sides of the target to guard against just such an incident."

I had many responses on the old board, and my thanks to you all once again. I have been continuing my research as and when possible since my initial posting, and have found a few more details.

I wrote to the RAF Air Historical Branch and they very kindly forwarded to me a report, Bomber Command Report on Night Operations, Night Raid Report No. 609, dated 2 September 1944. In Section 9 of this report reference is made to a possible collision ("The Master Bomber and his deputy were both lost over the target, possibly in a collision."). Later, in Section 19, reference is made to a collision ("2 of the Le Mans losses were caused by a collision, and the third by light flak S. of the target. These included the Master Bomber and his deputy."). This report is the earliest source document I have been able to find that mentions a collision.

I also wrote to Stuart Hadaway, a curator at the RAF Museum at Hendon, after reading his excellent book "Missing believed killed". Mr Hadaway was kind enough to forward copies of aircraft loss report forms for both JB653 (my Uncle's aircraft) and ND845 (the Master Bomber's aircraft) which make no mention of collision whatsoever.

At some point between 20 May 1944 and 2 September 1944, therefore, there was likely to have been a report (debriefing? intelligence?) that raised the possibility of a collision. My questions are, what form might this report have taken? Is it likely that the information survives today in a publicly accessible form? Where might I hope to look in order to continue my research?

As I said originally, I have an electronic copy of Bill's Flying Log Book (my mother has the original) and would be happy to send a copy on CD to any researcher or historian who has an interest.

All the best