17cm(?) German (?) projectile ID help needed

This supposedly WW1 souvenir was recently donated to a museum that needs help cataloging it.
Diameter about 6.8 inches, and about 32 inches long. Markings include a crown over M in two places, GwK over widely space III and 18. Several pairs of “matching numbers”(?) on the body and upper sections. Extreme tip is a tiny screw off point, not a fuze. Two copper rotating bands with a shallow crimping groove(?) below the lower band. Rear section below that bands tapers slightly. Traces of brown paint on the body, but no stenciled markings visible.
Any help would be appreciated.

It is an Imperial German Navy shell. This 17cm L/40 guns are
mainly used in coastal defence, as railway gun or on a wheel mount.
In WW. ! the railway guns and coastal defences where managed by the Navy.

John, congratulations, this one is impossible to get over here in Germany.
Are you sure you have no fuze in there (below the ballistic cap)? I’m just curious what is on this shell if so.

Here the two versions:
No1 is the HE and No2 is the chemical shell:

And here the 1940 manual to download: