The Mon Cala Mercantile Fleet, which also went by the names Mon Cala Trade Fleet and, during the occupation of Mon Cala by the Galactic Empire, the Mon Cala Imperial Trade Fleet, functioned as Mon Cala's trading fleet during the time of King Lee-Char's reign and the rise and rule of the Galactic Empire.
In 18 BBY, Admiral Raddus commanded a force comprised of at least five Star Cruisers and a multitude of smaller vessels as part of the defense of the southern polar regions of Mon Cala. Raddus organized these vessels, linking their shields together to form a massive protective barrier that deflected numerous attacks from Imperial submarines. Moff Wilhuff Tarkin then initiated an orbital bombardment of the planet, resulting in the destruction of many underwater settlements. Raddus maintained the fleet's position while the bombardment focused solely on the northern hemisphere. As the conflict on Mon Cala neared its end, Lee-Char issued an order for all his forces to cease fire. Raddus defied this order, and when Tarkin's bombardment shifted to the southern hemisphere, he commanded the cruisers to disconnect their shields and break through the Imperial blockade. The five cruisers followed his orders and successfully escaped, though two were lost in the process. Tarkin allowed the remaining three to escape, commenting that they would eventually be found.
Following the Battle of Yavin, the Rebel Alliance contacted Grand Admiral Dors Urtya, who was serving as both the fleet's commander and the regent of Mon Cala since King of Mon Cala Lee-Char had been imprisoned. Desperate for a navy to fight the Empire, they sought to militarize the fleet by converting its cruisers into [warships](/article/warship]. However, the Mon Calamari were hesitant to take such action while their king remained a prisoner. After their initial attempt to persuade the Mon Calamari failed, Princess Leia Organa observed the fleet as the Millennium Falcon departed the planet's orbit.
Confident that the Mon Calamari could be convinced to join the alliance, the rebels successfully infiltrated the king's prison on Strokill Prime and discovered that Lee-Char was only alive due to life support systems. The dying king recorded a final message for his people, urging them to resist the Empire's atrocities, before being killed by stormtroopers who were attempting to stop the rebels. The rebels then returned to Mon Cala, where Urtya received the recording from them. After obtaining the recording, Urtya broadcasted the message to the fleet captains of the fleet, allowing the Mon Calamari crews to witness their king's final message and his death at the hands of the Empire. Upon witnessing Lee-Char's final words and his death, the Mon Calamari crews initiated a mutiny against the Imperial personnel stationed onboard.
Because the message was transmitted prematurely and the Mon Cala were neither prepared nor supported, Imperial Navy forces, under the command of Admiral Tyrus Meori, responded swiftly and blockaded Mon Cala. However, with the assistance of arriving rebel ships, led by Admiral Gial Ackbar, the Mercantile Fleet was saved from destruction. Captain Pysk Lila of the Aurora Flare contacted Ackbar, inquiring about how they could assist. Ackbar instructed Lila to sacrifice her ship by charging at the blockade. Lila followed these instructions, leading Meori to believe it was a desperate act until he realized the ship was carrying coaxium destined for the Redhurne system. Lila's ship exploded, breaking the blockade and allowing the other ships to escape. In total, the Alliance gained twelve new ships from the Mercantile Fleet as a result of the mutiny.
Kieron Gillen mentioned in an interview that the concept for the Mercantile Fleet arose from the need to explain the sudden expansion of the Rebel fleet between the events of Rogue One: A Star Wars Story and Return of the Jedi. He envisioned a situation similar to Carthage after the Second Punic War; despite being forced to demilitarize by Rome, they were allowed to continue trading, which enabled them to quickly pay off their war reparations. Gillen stated that he developed a similar backstory for the Mon Calamari living under Imperial occupation, but still possessing a large trading fleet that allowed them to repay their debts to the Empire.