The "flat dome" canteen cap - releases from 1913 to 1914.
Aluminium canteen caps, manufactured Rock - Island military Arsenal:
1) Early cap, produced until 1913.
2) "Flat dome" of pressed aluminum, produced in the period from 1913 to 1914.
3) "Dome cap", standardized in 1914.
Your canteen - made in Rock-Island military Arsenal, in the period from 1913 to 1914.
There are also differences in the ring that the chain attaches to, that might give a clue.
Yes, on this photo is also clearly visible. "Ring" in the photo number 3 appeared in 1914.
# 3 resembles the one I posted..
P.S. Great information Gents
I'd rather be A "RaD Man than a Mad Man "
Thanks for the info!!! You are all awesome!! I am loving this forum already.
PS I forgot to write about the canteen cover - covers of this type (with a side seam), manufactured since 1941. You have a good cover of the Second World War.
Now you'll just need any pre-1945 dated cup to complete a nice WW2-era set.