Tanks who play on controller.

[Mikey_R]

Hold L2 and press R1 and you will cycle through the enemies on the screen. Or Hold R2 and press L1 and you will cycle the other way around.

Just to expand on this, you can hold either L2 or R2 and press L1 to cycle left and R1 to cycle right. So it is a bit more flexible than implied.