A Bronze hole

I bought a light tent off the internet. It's just a three foot cube! There's no way I'm going to be able to sleep in that.
Luckily it doubles up as a er... Oh, maybe you could call it... a light tent.
This is something we found on e beach a few years back. I'm guessing it's something nautical (there's not much gets past me) and maybe military. I also think it looks like something the Americans would have made. We British (well mostly the Scots) fancy ourselves as engineers but the reality is the the Americans could design and build a device to knock us into a cocked hat before we even knew it. They are much better at engineering. They made something superior to the Spitfire in about 6 months - start to finish... For instance.
Might have been a bit longer. Can't remember.
Anyway, I have found a use for this and will blip it when I've finished making the thing - in my quaint British way.