Cylindrical Grey Military Tube Cache?

I put the word military in there for this Cylindrical Grey Military Tube Cache? , since it reminded me of something military, though I'm not sure it was. Its metal, and very sturdy, plus it had a rubber seal on it, and the letters RM on the bottom, thats all I could read, also on the screw on lid there were two circles, I think there was a rope or chain attached here at one time. Nice cache container, I think it would float and it strong, and could fit in tree holes, and other slots.

Looks dangerous in this day and age, well not really.