The two small dimples on either side of the opener end of the lid on the M19A1 (or early M2A1) boxes held the lid partly open with cartridges ready for use while the side skirts kept out rain and dust.
WW2 style, era .30 cal ammo can for 192 rounds ammunition in 8 round M1 garand rifle clips and bandoleers. Makers placed the welded seam of the box on the opener end and their initials on the hinge end. UNITED placed the welded seam on the hinge end and their name will be found on the opener end. Color shades will vary- good used condition. Approx. measurements are 3-3/4″ x 10-3/4″ x 7″