Complex sentence: Repeated calls by the British for the Japanese to surrender were ignored: the Marines holding the perimeter shot any Japanese attempting to escape, while within the swampland hundreds of soldiers died over the course of several days for lack of food or drinking water.
Split into simpler sentences: Repeated calls by the British for the Japanese to surrender were ignored. The Marines holding the perimeter shot any Japanese attempting to escape, while within the swampland hundreds of Japanese soldiers died over the course of several days for lack of food or drinking water.