I have some US military canteen cups with various codes between the 2 handles.

The 1st one is stainless steel weighs 244g and says "US RJS",
the 2nd one weighs 224g and says "US 88 PAC FAB",
the 3rd one weighs 238g and says "US 89 WWM"

Can anyone tell me what the codes mean?

The first is definitely stainless steel the other two have never been used,I'm not sure if they are aluminium they feel too heavy.
How can I tell what metal it without drilling a hole in them.