This appears to be a 1955 Phantom "B". It is a stainless case with a black/Charcoal dial and silver hour markers and hands. The case back is marked with Bulova Stainless Steel Case AntiMagnetic Waterproof Shock Resistant Patent Pending L5 with a small dot after the 5. This is the first time I have seen a Bulova with a Pat Pending mark. I am wondering if the Pat Pending and dot after L5 signify something? This is a very thin watch and appears to be a monocase so I am not going to open it since it is running. I assume it has the 11ACC movement but not sure. This is a very attractive and comfortable Bulova watch.
In reply to This should have said Thin by JimDon5822
Agree with Phantom 'B'.
The inner case separates from the bezel. You may be able to separate them by pushing on the crystal while holding the bezel. This listing shows a photo of the separated parts. There is also a split-stem that can be separated in order to remove the movement from the case.
In reply to Agree with Phantom 'B'. The by Andersok
Patent Pending due to case and case design refinements. This was a highly competitive part of the watch world- coming up with water resistant designs, and very few did this in-house. A company would either hire or engage a designer and then a patent agreement would be worked out, sometimes the patent automatically was then owned by the company. Companies actually had staff/teams working on these sorts of things, but we can't say whether or not this was the case with Bulova.
Here is an example of a patent where the designer was working for Bulova:
https://www.mybulova.com/watches/1959-surf-king-8513