The Carigan defense was a defensive strategy that could be used to fight off invasion forces if a world did not have the luxury of full planetary shields. It was named after its inventor, Governor Carigan of the planet Bryx.

A large number of planetary guns would be deployed in the most important city of a planet, usually its capital. This forced an invading fleet to concentrate its ships in the space above the city in order to overwhelm its defenses, preventing the fleet from blockading the entire planet. Supply ships could then safely deliver supplies, weapons, and reinforcements from the other side of the planet. Elusive Leviathan Submersible Carriers were used to launch starfighter attacks against the enemy fleet. The fighters would engage the enemy, and then quickly flee back to the safety of the planet's atmosphere. Enemy ships that pursued them would be destroyed by fire from numerous planetary guns.

When the enemy finally launched their invasion, they would be in for a deadly surprise. Although the high concentration of planetary guns would be known from the start, the actual number of guns would be even higher than expected. Before the invasion, many guns would be hidden and kept from firing in order to conceal them from the enemy. Facing unexpected fire from numerous guns, the enemy would suffer enormous casualties, losing much of their invasion force before they even landed on the planet's surface.

Although the Carigan defense was highly effective, it was rarely used because it required a great deal of preparation time, and more weapons and resources than many worlds could afford.