At the beginning of March 1938, while it was undergoing a reorganization, the nationalists launched the Aragon Offensive through the Belchite sector. The 61st MB, still not fully equipped, was sent urgently to try to plug the enemy gap. It was temporarily attached to the 18th Army Corps, a formation that would end up retreating before strong enemy pressure. During this withdrawal, some forces of the 61st MB were isolated north of the Ebro River, although most of the unit became part of the 13th Army Corps. The unit continued to retreat towards the Maestrazgo, pursued by nationalist forces. By April 5, the brigade was located in Morella, where it established a defensive line together with the 52nd and 211st mixed brigades; however, one of the battalions of the 61st MB fled in disarray before the enemy attack, which led to the collapse of the entire front. This failure was mainly blamed on the 61st brigade. As a consequence, one of its officers was shot in the presence of the troops as a lesson.