Rolex Oyster SpeedKing - Underline Dial?

[murkeywaters]

Hi All,

Been a long time member here but have been more into other watches due to financial position but the funds are coming so hopefully will be a Rolex owner soon..

On to my question, a friend has a very small vintage Rolex - an Oyster SpeedKing, I can't seen to find out much info on this watch and previous questions on other forums have came up blank, so I was hoping someone here might be able to give me/my friend some more info on this particular watch..

It has an underline dial which is very different from what else I can see online, looks to date from around the mid 1940's and its about 29mm diameter, also I can see just a SWISS mark at the 6..

Any info would be greatly appreciated

Some pic's -