The C57BL strain was established by C.C. Little in 1921. C57BL/6 mice diverged from the C57BL strain in 1937, and were maintained at the Jackson Laboratories (6J). The C57BL/6N substrain diverged from the mice at the Jackson Laboratories in 1951, and was maintained at the NIH. C57BL/6N mice were sent to the Charles River Laboratory in 1974 (6NCrl), to Harlan Sprague Dawley in 1983 (6NHsd), and to Taconic Farms in 1991 (6NTac). Additionally, C57BL/6NCrl mice were transferred from the Charles River Laboratory to Japan in 1976 (6NCrlj), and later to Orient Inc., Korea in 2001 (6NCrljOri).