Hi Keith,
Unfortunately I cannot help you regarding your current investigation but I can provide you with some information on Herbert Altner. I was lucky enough to meet Herr Altner at Duxford back in 1996. Herr Altner and I were meeting with former No.57 Sqdn tail-gunner Len Manning who was shot down by Herbert during operations on the 18/19.07.44 in Lancaster JB318.
I hope you find the attachments of some use, I have not had time to add this loss to our remembrance pages, but it will be added over the winter months!
Kind regards,
Melvin
www.aircrewremembrancesociety.com