In April 1945 the 15th Brigade took over from the 7th Brigade and resumed the advance on the Hongorai and Mivo rivers. In early July, the 29th Brigade relieved the 15th and continued the advance and as they attempted to cross the Mivo, the Japanese launched a ferocious counter-attack upon the 15th Battalion which was turned back by desperate defence. Following this the advance came to a halt as torrential rain turned the axis of advance into "a sea of mud" and many of the bridges upon which the Australian supply system was dependent were washed away. As the situation became worse, briefly even patrolling operations had to be stopped. These patrols were resumed, however, in late July and into August, as isolated pockets of Japanese began to attack the 3rd Division's supply lines and support units. As preparations were made to resume the advance, the dropping of two atomic bombs on Hiroshima and Nagasaki and Japan's subsequent unconditional surrender brought the fighting on Bougainville to an end and a cease fire came into effect.