The second Fatimid invasion of Egypt occurred in 919–921, following the failure of the first attempt in 914–915. The expedition was again commanded by the Fatimid Caliphate's heir-apparent, al-Qa'im bi-Amr Allah. As during the previous attempt, the Fatimids captured Alexandria with ease. However, while the Abbasid garrison in Fustat was weaker and mutinous due to lack of pay, al-Qa'im did not exploit it for an immediate attack on the city, such as the one that had failed in 914. Instead, in March 920 the Fatimid navy was destroyed by the Abbasid fleet under Thamal al-Dulafi, and Abbasid reinforcements under Mu'nis al-Muzaffar arrived at Fustat. Nevertheless, in the summer of 920 al-Qa'im was able to capture the Fayyum Oasis, and in the spring of 921 extend his control over much of Upper Egypt as well, while Mu'nis avoided an open confrontation and remained at Fustat. During that time, both sides were engaged in a diplomatic and propaganda battle, with the Fatimids' in particular trying to sway the Muslim populace on their side, without success. The Fatimid expedition was condemned to failure when Thamal's fleet took Alexandria in May/June 921; when the Abbasid forces moved on Fayyum, al-Qa'im was forced to abandon it and flee west over the desert.