This is actually an Ordnance Department item. 15-19-98. Class 15, Division 19, Drawing 98. Class 15 is something of a catch-all. Most individual field gear was in Class 20. The Broad Head Hatchet was also in 15.
This case was for bits and pieces of stuff for the Browning Automatic Rifle. Except nothing is that specific. It was developed for the BAR, but was used for other small arms. The M-1903 rifle had a small parts wooden thing that could go in the butt. This was a step up from that. Stepping up from this, you get into tool and spare parts rolls. And then up into cases for them. The bigger the boom, the bigger the tools and spare parts sets.
Typical stuff found inside during the inter-war years.
The Standard Nomenclature for it.
Contents in 1918, when introduced.
Typical WW2 example. Every WW1 one I've seen was made by Jewell Belting Company. Located in Hartford, CT. Right down the road from Colt.