Any idea as to that Yarra photo's date? Is it 1941 or early 1942?
Is her pendant number clearly visible and it is unquestionably her?
Additionally can you confirm she still retains 2 single 4-inch in A and X positions?
Does the mount at B position resemble anything like the MG her sister ship Swan carried in B position by late war?
Here's one from my database showing it clearly at that time:
http://www.fileden.com/getfile.php?file_path=http://www.fileden.com/files/2008/6/1/1940009/HMAS%20Swan%20L74-U74%20Modified%20Grimsby%20Class%20Sloop.jpgI was only aware that B mount was replaced by a 40mm Bofors if and when these sloops got their single 4-inch guns removed and replaced with twin 4-inch mounts, or they got 0.5 Vickers in B position, so if you can confirm your photo is unquestionably Yarra during 1941 or 1942 it would then seem she differed to the other RAN ships of this class in this important feature.
I'm not sure why you mentioned a 3-inch mount Mike, as Yarra never had one fitted! Only the RN vessels had one in B position when completed, RAN Grimsby's did not.
This is why I prefer to consider these RAN Grimsby's as 'modified Grimsby's' as they were built slightly later, were some 16ft shorter, but heavier and shipped a different main armament fit.
Finally Hague's Sloops book confirms the only wartime photo I have of Yarra was taken in August 1941.
He further states:
"Yarra completed with three single 4inch HA and 1x Quad Vickers, probably still in that state when lost".
Well I've already showed above the 0.5 vickers was not there when first commissioned and instead was added later between 1936-39, one wonders if your rare wartime photo of Yarra proves Hague was additionally wrong and B mount was in fact replaced by an MG at time of loss.
Look forward to your reply on these interesting warships.
Kind Regards
LB