The case has L1. The movement looks like L5.
Hi Peter Smith. It looks like you have a Duo-Wind case. According to the movement data base listed on here the !0CSC was made between 1952 to 1954. And yours is an L5. So apparently they were made for one more year. Your watch could have had a movement swap or the rotor could have been replaced. Good possibility the movement has been swapped because the Duo-Wind had "Duo-Wind" printed on the dial and yours has "Selfwinding" printed on it.
Probably is a duo wind. I agree on the probable movement switch.
This case can be found used in the Duo Wind (both luminous 'G' and non-luminous 'F' dials) and the Thayer model (not found in any ad before 1952, and is the non-luminous type with Selfwinding on the dial); so if we use the case as our date of this watch, 1951, we can rule out Thayer, leaving us with Duo Wind - without any variant, since we do not know what the original dial was (Selfwinding cannot be found in any Duo Wind ad before 1952 so the current dial is most likely not original, and not from a Thayer which was non-luminous). Also the design of the 6 is different than any of those found in the ads using this case; looks more like a dial from the Clipper line.
1951 Duo WInd (likely with dial and movement swap)
Interesting that self-winding wasn't mentioned in earlier the ads, doesn't Duo-Wind MEAN hand and kinetic winding?
Geoff, to clarify - Selfwinding was mentioned in the early ads, just not printed on the dial in any pre-1952 ad that I can find.
Duo wind was used to describe automatic winding in both directions.
I think it's a Duo-Wind as well. To Alan's point it might be as simple as a new rotor.
Agree with Dou-Wind also
Duo wind, movt and dial 1955, case 1951, not that unusual a swap.