Rolex 2635 1930's stainless steel case info...

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Hi,
I just bought the following Rolex ref 2635 from around the early 1930's. It's a two piece case which you can't find a lot of information on this particular steel ref. Was this style of case meant to enhance waterproofing? Case is around 30mm excluding the crown.
Any information would be great.
Cheers Russell.