In August, the Ottoman military, led by the Army of Islam, launched a new assault against the frontline positions, which were primarily manned by Armenians. Despite some initial victories, the Armenians had to retreat. The size of the British expeditionary force had proved ultimately to be too small to make much of an impact in the defense of Baku. In the first week of September, a joint Ottoman-Azerbaijani force composed of 15,000 men advanced without much resistance toward Baku and by September 13, had reached the suburbs of the city; meanwhile, Baku's Muslim population prepared to welcome the entry of the Ottoman army. The remaining Armenian troops were too ill-prepared to halt the advance and Dunsterville refused to retain his force any longer. On September 14 his force evacuated from Baku and sailed to Enzeli, leaving the city virtually defenseless.