Ok, I can answer a few of the questions now, and then examine the inside of the canteen or whatever it is a bit later...my son-in-law took the leather cover off last night and he said that it had 1943 on the container MK II and No. 3 were also on it. He advises not to take off the leather case any more since the strap looked rather fragile and stiff and might end up breaking off.
Remember, I"m an artist, not a specialist in antiques and metals like most of you, but he said that the larger screw-off lid on top is brass. The chain seems to me to be a lighter material then brass but I could be wrong. Also, I was examining it last night and the inside of the post does have a narrow hole in it. I will get a flashlight and see what I can find inside the container in a bit,
Thanks,
Diane