[Larry]

I hasve just looked at a book Battle-Axe Blenheims, 105 Sqn RAF at War 1940-41' by Stuart Scott published by Alan Sutton Publishing Ltd c 1996

In the book there is plenty of evidence of Blenheims Mk IV in 1940 with small sized under nose gun barbets - which are more streamlined that the later square versions see with two rear facing machine guns. I see no reason why 139 Sqn which worked so closely with 105 Sqn, should not be similarly equipped. 82 Sqn Blenheims also had the same barbet in 1940