During their occupation the Japanese developed Rabaul into a much more powerful base than the Australians had planned after the 1937 volcanic eruptions, with long-term consequences for the town in the post-war period. The Japanese army dug many kilometres of tunnels as shelter from Allied air attacks, such as the bombing of November 1943. They also expanded the facilities by constructing army barracks and support structures. By 1943 there were about 110,000 Japanese troops based in Rabaul.