I'm seeking help with any information on these 1931 USN Bureau of Ordnance NGF (Naval Gun Factory) 10x40 Mk XII No. 4 binoculars. The Mark XIIs on Peter Abrahams' 1996 Bureau of Navy BUSHIPS binocular list are 10x45s. This pair is marked Bureau of Ordnance so that might be why it doesn't show up on the BUSHIPS binocular list.
That's all I have so far. I can't seem to find another image or reference, though my internet search skills are not the best.
I'm wondering what might be their story. Are there other USN bent shoulders out there? Were they built at NGF in collaboration with another company? Are 10x40 bent shoulders part of any known binocular lineage?
Thanks in advance for your interest and help.