Metal Boxes stamped 1914-1918

I’ve got an unusual one to try and ID.
A friend tonight showed me five tinplate boxes each about the size of a pack of playing cards but about twice as deep. Each lift off lid is embossed with a date about 3/4" high on it, one is 1914, one is 1915, and so on through to 1918.

There is some evidence there might have been a paper label or wrapper stuck on each at some time which has been removed.

The boxes look old enough to be contemporary.

I don’t know if they are even ammunition related, I suspect probably not but the connection to WW1 is obvious.

Has anyone got any ideas?

Just a wag, but maybe a food ration box/tin. The wrapper would have identified the contents. Date, obvious.