25.6 SOB inside, I'll probably be able to say more about it when I have access to my documentation on sunday. From memory, this case shape was proposes by Denison in the 30's in England. Is the caseback signed Oméga?
I could have been a little too quick, it could also be a 23.7S inside. Can you read what's written under the balance wheel? If not, can you measure the diameter of the movement?
Could be US market piece, but I vote that it is a recase. It was common for US retailers to get movement and cases separately and make their own dials. Something about the whole piece doesn't seem to match up. Still an interesting watch. gatorcpa