We need them.
12.7mm Guns: 50 cal. Machine guns for ripping fighters and light armors apart.
20mm Guns: Slightly stronger than the 50 cal. fires at a little slower rate, good for gunboats
30mm Guns: Heavier and stronger than 50 cal and 20mm . Fires at a lower rate tho
50mm Guns: Much slower fire , packs a bigger punch.