Comments:
I don't know...
Claret has been openly credited with the original San Marco minute repeaters, and the Hourstriker shares its Jacquemart feature so it makes sense that he could have been involved with its development. On the other hand Dubois-Depraz specializes in developing and manufacturing add-on complications modules for ETA movements like the one in the Hourstriker, so it also makes sense that they were involved too. Maybe the likely scenario is that both were involved.
I think the UN is different from the Vacherons...
Fwiw I found the UN repeater auction info:
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Manufacturer: Ulysse Nardin
Year: 1950
Movement No: 127'544
Case No: 668'852
Material: 18K yellow gold
Calibre: Manual, cal. 12"', 27 jewels
Bracelet/Strap: Leather
Clasp/Buckle: Yellow gold plated pin buckle
Dimensions: 36mm diameter
Signed: Case, dial and movement signed
Accessories: Accompanied by Ulysse Nardin Extract from the Archives confirming production in 1950
It is a 12 ligne movement; the Vacherons are 13 ligne without a sub seconds dial. I found a 35mm Vacheron from the 1950's that has a 12 ligne movement with sub seconds. I think it is likely the same movement as the UN:
