From Command and Conquer Wiki
A first generation SAM Site
SAM stands for Surface-to-Air Missile. SAM sites, structures that fire such missiles, are constructed to provide defense against aerial threats. During the Great World War II the Soviets constructed SAM Sites to defend their installations from air attack. In more recent times both the Global Defense Initiative and the Brotherhood of Nod have constructed SAM sites, but SAMs were originally constructed only by Nod, and the situation is similar again in the Third Tiberium War. SAM missiles are generally very accurate, capable of hitting airborne hostiles as they head towards a certain target.
SAMs were lucrative targets during the First Tiberium War. Nod forces constructed many throughout the lands that they controlled, threatening all air power of those who opposed them; namely, GDI's YF-23 Black Widows and C-130s. GDI forces often had to assault these positions in order to ready the locations for aerial reinforcements or A-10 support. However, for this reason, Nod guarded these SAM sites with much zeal.
In the Second Tiberium War, Nod used traditional SAM sites, while GDI used the SAM Upgrade to their Component Towers, as both sides had acquired air power by this time. GDI had their famed Orcas, while Nod acquired Harpies and Banshees, fighters and bombers respectively.
During the Third Tiberium War, GDI resorted to AA Batteries but Rigs had SAM launchers for AA Duty, while Nod forces continued to construct SAM sites. However, SAM sites are now constructed according to the new Nod 'hub' base defense system, whereby defensive structures - such as SAM sites - are built in groups of 3 with a central 'master' hub repairing and even replacing damaged towers as necessary. It should be noted, however, that if this hub is destroyed all slave structures will be taken down along with it. In all three wars the SAM sites should not have enemy ground units attacking it even if its infantry.
