WW2 Thompson 50 Round Drum Pouch with shoulder strap, these were manufactured by a number of different manufacturers, the early design had no shoulder strap and only had a rear belt loop to carry it. Stamped with U.S on the front flap and Manufacturer Markings and Date on the inside of the front flap.
This pouch was manufactured by Boyle in NOS un-issued condition but not dated, this is a harder to find pouch with these markings and very desirable.