The operation to retake Wall Maria (ウォール・マリア奪還作戦 Wōru Maria Dakkan Sakusen?) was a mission assigned by the royal government in which twenty percent of the human population that remained after the fall of Wall Maria were sent out to reclaim land. In truth, the operation was carried out in order to alleviate the food shortage brought on by the significant loss of territory and influx of refugees from Wall Maria. A tremendous number of people died during the operation at the hands of the Titans, as its secret goal had always been.
In an attempt to reduce the severity of the food shortage riddling Wall Rose, the royal government sent out 250,000 soldiers and civilians from Wall Maria back out to reclaim the lost lands from the Titans.
In the aftermath of the operation, of the 250,000 soldiers and civilians sent to reclaim Wall Maria, less than 200 made it back alive. This resulted in the loss of a fifth of the total population of the Walls, but in turn, alleviated the food shortage that followed after the Fall of Wall Maria.
It is later confirmed by Dot Pyxis during the Battle of Trost that the operation to reclaim Wall Maria was nothing more than a ploy by the royal government to cut the population in order to alleviate the food shortage crisis of Wall Rose.