Surface-to-air rocks, also known as surface-to-surface rocks when used alternatively, are projectiles used as the primary weapons of the Royal Earthbender Guards. Usually launched from the watchtowers outside of the Earth Kingdom Royal Palace, these large earthen spheres are used both as offensive and defensive armaments.
The purpose of surface-to-air rocks is to prevent intruders from entering the royal palace. Primarily used as surface-to-surface rocks to halt invaders on foot, the spheres can also effectively be used to ward off an aerial assault. The rocks are large frustums prepared by the dozens. When launched, these projectiles are flipped so that the small jutted side impacts the target first. This is advantageous as the rock's positioning makes it less likely for intruders to dodge the attack.
Once possible threats to the Earth King's safety are spotted, several of these rocks are lined up and fired in quick succession so as to effectively prevent invaders from bypassing the palace's defenses.
After arriving in Ba Sing Se, Team Avatar set off to find Earth King Kuei to gain his support for a planned invasion of the Fire Nation Capital. However, while attempting to do so, the team faced a variety of problems including a conspiracy theory which kept the Earth King from involving himself in any military actions. In a last-ditch effort to notify Earth King Kuei of an upcoming solar eclipse that would render firebenders powerless, Team Avatar decided to forsake every diplomatic approach and breach the palace by force. Immediately after entering the stronghold's perimeters, Royal Earthbender Guards targeted Appa and fired several stone frustum at him. The bison dodged several of the projectiles and those he could not dodge were destroyed by Aang through the use of earthbending; Team Avatar managed to land with relative ease, continuing on toward the palace.
- Surface-to-air rocks (or SARs) and their alternative use as surface-to-surface rocks share their namesakes with real-world weapons; surface-to-air missiles and surface-to-surface missiles (SAMs and SSMs respectively).
- A surface-to-air rock is fired by the joined effort of four earthbenders: two benders lift the object in the air, and two more propel it at the incoming invaders.
- These are similar to the rock-based projectiles used in pro-bending.