Koumi Line was a local line running through high land area (Yatsugatake Kougen) of middle Honsyuu (Main Island), surrounded by beautiful mountains, and ran at the highest altitude of all JNR lines, 1375m. The line was a low grade local line and only limited light weight locos were allowed.The locos used were C56 class. The area was not far from Tokyo and popular summer resort for Tokyo residents.
JNR C56 Class
C56 was a small tender loco designed for low grade local lines and 160 of them were built from 1935 to 1939. Actually this class was a derivative of light tank engine C12 class. To extend the operation range of C12 class, tanks were removed and a small tender was fitted. Many small local lines might not be prepared with turntables. So the tender has cut-outs on both sides to provide good vision for backing up operation. However the class had a tendency to derail on backing operation because of lacking trailing pony truck and rarely used in backing operation. More than half of them were sent to south-east Asia in WWII for military operation because of their light axle weight was suitable for such a purpose, and only one of them could return to Japan after the war.