The shield generator is a structure employed by both the Alliance and the Galactic Empire. Shield generators produce a translucent bubble surrounding a ground base, through which energy projectiles cannot pass, forcing the enemy to physically pass through the shield to engage. Solid projectiles, however, such as missiles and mass driver salvos, can and will pass through the shield. When playing a Land Skirmish, the shield generator can be upgraded so that no projectiles can pass through it. It is important to note that shield generators are completely dependent upon power generators, which are often placed conveniently outside the shield's reach.