What is this?
This is a water-tight lantern made by Jay Moulding. It was commissioned by the United States Navy and it is intended to be used under water.
Why is it yellow?
We don't exactly know why it is yellow, it could be made in a bright color for visibility. We do know that the man who we acquired this piece from had about 10 and all were yellow. In fact, lamps like this are still on the market today, and they are all yellow.