Suga taught English as a lecturer at the Hiroshima High School of Technology (now the Department of Technology, Hiroshima University), Japan, before he was called back to active service in 1937, to serve in the Second Sino-Japanese War. He became ill with diabetes and retired again in October 1941. After the Japanese attack on Pearl Harbor, Suga volunteered for service as a prison camp commander on an advice of his younger brother, believing that his language skills would prove useful. He was appointed commander of all POW and internment camps in Borneo.