The Fire Navy blockade was a strategic naval blockade stationed within the Mo Ce Sea, serving as a barrier with the purposes of protecting and controlling entrance to Fire Nation waters. The blockade consisted of hundreds of Fire Nation cruisers that patrolled north to south, guarding the maritime passage between the Fire Nation and Earth Kingdom. The blockade had orders to fire upon any unauthorized vessel approaching Fire Nation territory. The then-CommanderZhao was placed in command of the blockade when it was first encountered by Team Avatar with PrinceZuko on their trail.
While trying to reach the Fire Temple in time for the winter solstice, Team Avatar attempted entry into the Fire Nation by air, but they encountered the blockade and were consequently fired upon by order of Zhao. The fact that Prince Zuko was also in pursuit of the Avatar and about to be caught in the attack was of no concern to Zhao, not only because of their rivalry, but also because Zuko was banished from the Fire Nation and was not permitted in Fire Nation territory. During the attempt to stop Team Avatar's advance, the engines of Zuko's ship were badly damaged by a fire ball. When Team Avatar managed to pass the blockade, Zhao allowed Zuko to pass through as well in the hopes he would lead him to the Avatar's destination.
Later, after waking from a coma, Aang attempted to enter the Fire Nation alone, not wanting to put his companions in danger. Using waterbending, Aang simply swam under the blockade into Fire Nation waters without being spotted. While in pursuit, the rest of the gang later flew on Appa over the blockade.
During the Day of Black Sun, the invasion force succeeded in passing the blockade with a large screen of steam bent by the Foggy Swamp Tribe's waterbenders. The invasion force entered the Fire Nation without incident and reunited with the rest of the force stationed at the Black Cliffs.