Combat Helmets
Combat helmets were a favorite design motif. Most of them were non-specific;
that is, they were meant not as an accurate depiction of a certain helmet but
rather as a general symbol of the military.

Most helmets you will see are Army steel helmets with the Army star in the front.
Less often a Navy helmet will appear and these have either an anchor or a cherry
blossom in place of a star.

In
Japanese Military Sake Cups Fuller identifies the four types of helmets, and
since he obviously knows more about them than I do, I'll quote from his book:

'There seems to have been four patterns of steel helmet:
c 1917 pat.- Conical with a narrow visor in the front
c 1928 pat. - Bowl with a pronounced brim somewhat similar to the British pattern
but not as flat
c 1931 pat. - Domed with a sloping brim of equal width all around
c 1938 pat. -Slightly more conical than the c 1931 pattern and a less pronounced
but more sloping brim.

The last two patterns are hard to separate on cups but at least establish a post
1931 date.'                                
 (page 32)

The colors of the helmets vary, too. I have seen gold, brown, silver, and green
helmets on cups. I suspect that these were stylistic variations.
Inscribed 'China Incident, Victorious
Return Commemorative'.
Inscribed 'China Incident
Commemorative'.
Inscribed 'Incident Commemorative'. I guess
they forgot to stamp in which incident this
refers to.
Inscribed 'Victorious Return
Commemorative, The Glory of the Country'.
The inscription reads, 'Manchurian
Incident, Victorious Return
Commemorative'.
Inscribed '16th Infantry, Discharge Commemorative'.
No star on this helmet.
The helmet here is colored green, though
I am not sure if that means anything.  
Inscribed 'Short Service, Discharge
Commemorative'.
Rare pewter cup with polished helmets,
each with a painted gold star.
Embossed kanji on the reverse read  
'Victorious Return Commemorative,
Showa 7 [1932] March'.
No star.
Green star.
Uncommon silver-colored helmet.
Embossed and painted cherry
blossoms and combat helmet.
This helmet has a blossom
where the Army star should be.
Rare Pacific War era bottle.
Inscribed 'Great East Asia War.' The kanji on the
helmet means 'Loyalty.'