and a Google search will turn up the owner's manual. That s/n is from the 1950s so perhaps the box also mentions Vacheron & Constantin? If so, that was a marketing partnership for North America (research the Galaxy wrist watch for a similar situation) and doesn't identify the clock as a V&C. Hope this helps, please post a picture of the V&C marked bits.
Picture from the 'net. Vacheron & Constantin-LeCoultre Watches, Inc. was a company started by Longines-Wittnauer Watch Co. of New York to market products in North America. It was a necessary replacement following the demise of V&C's previous American agent, Edmond E. Robert Co., and not coincidentally came with the merger of JLC and V&C. This distribution arrangement also led to the assignment of VXN as their shared American importation code found on the movements of LeCoultre and V&C watches sold in the USA from 1938 to 1965. As you can appreciate, these "name games" continue to cause much confusion in the marketplace.