The Battle of Bryx took place on Bryx between Governor Carigan and the Galactic Empire. Carigan had purchased several Leviathan Submersible Carriers and owned hundreds of hidden grounded anti-aircraft guns as well as many other types of high-tech weapons. The battle led to the defensive strategy known as the Carigan defense.
First the Imperials attempted an orbital siege to attack the Leviathan Submersible Carriers whenever they surfaced. However, whenever Imperial ships descended upon a Leviathan, they came under heavy fire from the hidden anti-air batteries. Moreover Carigan's fighters would stay within range of the ground batteries, thus gaining substantial supporting fire while attacking the Imperials. Imperials that attempted to pursue Carigan's fighters back into the atmosphere were typically shot down.
The Imperial commander pulled back into an objective orbit over the capital of Bryx, which allowed Carigan to receive supplies from the other side of the planet. Any attempt to stop his transport ships were thwarted by his fighters. He also purchased further armaments.
Having learned of Carigan's reinforcements, the Imperial commander decided that only a quick attack would lead the Imperials to victory. And so, he decided to bombard the capital and many of the planetary guns whose locations were known.
After the bombardment, a planetary invasion was commenced, using thousands of dropships. However, Carigan had avoided using many of his ground guns during the entire conflict, and their locations had remained unknown, until he started firing them at the Imperial dropships. It was estimated that at least 25,000 stormtroopers perished in the hail of blaster bolts, before they even set foot on the surface of Bryx.
Eventually, the Empire managed to land enough troops to engage in ground combat, but even then, they were disadvantaged, as Bryx's troops knew the combat ground much better and had the support of the population. The Imperials managed to secure the major urban centers, but there was still resistance from many of the Leviathan Submersible Carriers. Leviathans continued to offer resistance three years after the Imperial conquest of Bryx till the last one was destroyed due to a fault in its oxygen tank.