Chengdu became a military center for the KMT to regroup in the War of Resistance. Chengdu was beyond the reach of the Imperial Japanese ground forces and escort fighter planes. However, the Japanese frequently flew in the then-highly advanced twin-engine long-ranged G3M "Nell" medium bombers to conduct massive aerial bombardments of both civilian and military targets in Chongqing and Chengdu. The massed formation of the G3M bombers provided heavy firepower against Chinese fighter planes assigned to the defense of Chongqing and Chengdu, which continued to cause problems for the Japanese attacks.