This is a skin for the MP5A4 item. You will be able to apply this skin when you craft the item in game.
The MP5A4 is a craftable, military-grade 30-round submachine gun. Dealing moderate to low damage with low recoil which makes it extremely effective at close range. However, the MP5A4 has one of the widest spreads in the game, limiting its use to short range. Although, like the LR300, this can be countered with a lasersight, making it viable for medium-range combat.
The MP5 is currently the only craftable military-grade weapon.