Why

The  is a Testbed Misc tank.

Design
The tank has 4 Rocket Booster turrets on top of it arranged like the turrets of Swivel-4.

Technical
All of the turrets work just like Rocket Booster, with more of their thrusters activating the longer you hold fire. Since the tank is a Swivel-type tank, all of the turrets can turn a full 360 degrees.