Koch returned to the East Indies operation, and on 30 January 1942, when in command of "Corio", he was shot down off Timor by seven Japanese Zeros whilst carrying out a relief flight to Surabaya, Dutch East Indies. Of the eighteen people on board, five survived. Koch was wounded by gunfire in the left leg and left arm, and broke his right leg in the subsequent crash landing. Despite the injuries, he swam about five miles to the shore where he was looked after by local people, until the Dutch Navy found the survivors some days later, and rescued them with a Dornier flying boat. Some three weeks later, he was in Darwin hospital on the day of the first Japanese raid on Darwin. By good fortune, the QEA flying boat "Camilla" survived the raid, and Koch was flown to Sydney for treatment.