WWII Casings

A number of years ago I spent several years living and working out in Dutch Harbor.
I spent much of my free time exploring by hiking, skiing and paddling kayak around Unalaska Isl.
While beach combing after storms, I found the 3 ~2" dia. casings on Hog Isl., and what I assume is a .50 cal casing, on the beach along the village of Unalaska.
https://www.milsurps.com/images/impo...asings01-1.jpg
https://www.milsurps.com/images/impo...asings02-1.jpg

I have often Imagined that these casings were left over from the defense against the attacks by the Japanese. The only proof of that is in my mind. Plus, I have walked the deck of the USS Northwestern.
https://www.milsurps.com/images/impo...682d4efd-1.jpg

So much for reminiscing.
My question is:
What are the larger casings?
Can anyone identify them for me?

The cartridge case on the far right would appear to be Japanese as they used a rebated rimless case in some of their 20mm aircraft m/gs. it would be better to post a ruler for better id next to the cases

IMHO the rh case looks like a 20mm Oerlikon.

Agreed, the right one would be someone's 20mm with a rebated rim like that.

Thanks for the input guys.
It's been a busy week and days are getting shorter.
I haven't had time or light to get back on this until today.

OK here are the casings with a ruler:
https://www.milsurps.com/images/impo...asings03-1.jpg
The 2 copper colored 2" casings have a head dia of 1.945" [49.4mm]
The green verdigris casing has a head dia of 2.20" [55.88mm] with a distinct beveled edge.


The 20mm casing mics out to:
Head dia = 0.860" [21.85mm]
Max casing dia = 0.985" [25.02mm]
extractor groove flat = 0.082" [2mm]
And the head stamp after lightly scotch-brighting it look like so:
https://www.milsurps.com/images/impo...sings041-1.jpg
The head stamp makes me think that it may not be Japanese.

I'm still looking for a positive ID on all of the casings.

It was a large operation with far reaching effects. Long occupation, relatively speaking. Lots of different weapons were there and not just battle but practice happened. The 20 looks like standard US fodder and I'm thinking the large ones are maybe 30mm or 37mm. Both are close to the same type casing depending on which weapon they were used in. More people will be along, just wait...

Yeah, a lot was going on then.
In looking around, I found that the night after the 1st attack a lot of gun emplacements were moved around. It is possible that some might have been moved to the village area. There are still pillboxes along the beach by the village.

EDIT #1
I also found this photo:
http://www.researcheratlarge.com/Pac...chHarbor01.jpg
The markings show a number of Navy 20mm gun emplacements.

EDIT #2
Plus, Hog Isl. is just off the left edge of the photo.
The markings also show a number of 37mm emplacements on Amaknak Isl. There probably were some on Hog Isl. also.

All that helps to explain the artifacts.

They appear to be what's left of either 40mm or 37mm Anti Aircraft Artillery rounds. The Smaller may be 20mm cannon shell. They are badly corroded and I can't read the Markings on the case heads.