Is this a shell

So i'm stationed in okinawa and found this. Its made of hardened clay, but not heated as I can still push my nail into it. Its hard as a rock though. I speculate that a shell hit the mud and the actual shell corroded away due to the metal bits inside of it, leaving the shape.
http://imgur.com/a/Sx8fR

 

Looks similar to a WW1 era's artillery shell nose cone.

Here is a piece of Trench Art using something similar. My guess, for what its worth...

 

Was such used during the bombardment of okinawa?

 

Metal would not corrode completely away that fast...There is still an estimated 2,000 tons of unexploded ordnance remaining on Okinawa.


Wood, however would have completely decomposed over that time.

or, it could just be a cup, which I kinda doubt since it lacks a flat bottom.

 

Well it washed up, so I assume it had been in the water quite some time.

 

is there anything else similar in shape that could've done that?? may I ask what unit you are with...I was USMC 82'-90'...not Oki though...you are on a historic battlefield......lucky you

 

Im detached to the hospital. Not really sure what else it could be.

 

I'd ask a local. It's probably a local item made for some household purpose.

 

detached from what parent unit?