Because Inchon harbor was so shallow and muddy, the timing of the invasion had to be synchronized precisely with the autumn high tides so landing craft could make it to the shore without running aground on the mud flats. In addition, Wolmi-do (Wolmi Island) provided defenders with a strong garrison flanking the harbor. In spite of intelligence warning of the attack, the overextended North Korean army was unable to maintain a strong defense. The city fell with Allied losses of only 20 dead and 179 wounded.