WW2 Relic ,Crete 1941, but what gun?

Hi my friends !!! in my Sunday walk with my sons at an area that at 1942 a huge German camp and ammunition storage was we found this shell…It is 45 mm ,but in what gun was in use???
Thank you very much!!!

(at the bottom has 3 small holes)

https://i.imgur.com/hALoqlP.jpg

https://i.imgur.com/j9I60j5.jpg

You would need to show us the headstamp of that one.

I think I know what it is but do not want to put out guesswork when all we need is visible on the hs.

One moment my friend!!!Now someone told me that the base is 45mm,but the caliber of the gun may be 37mm…

Here you are!!!Thank you very much!!!

P1010001

Yes, it is a 37x265B case for the Flak 18, Flak 36 or Flak 43.
These were anti-aircraft guns.
And then there was the 3,7cm BK which was an aircraft gun and basically was a modified Flak 18.

Τhank you very much!!!