Without enough quad guns to go around, the Allies needed a smaller anti-air alternative that could be attached to existing vehicles. The answer came in the X-3 Rocket. Its lightweight and fire-and-forget mechanics make it an effective solution to most air threats.
This cheap plug brings the bang for the buck. Place this in any unit to instantly make airplanes think twice. However, any units with difficulties against Armor Type 1 or 2 enemies might also consider this plug. It's 2, 2 die attacks make is a menace at close range.
Consider this for some of your more target-able armor. If Blight planes are in the air, they could be coming for your VP spewing, muscle tanks.