The SNCF Class BB 66600 is a small class of centre cab diesel locomotives rebuilt from the earlier Class BB 66000 by fitting a slightly more powerful engine. The locomotives were long and weighed . Powered by an SEMT 12PA4 diesel engine developing , they had a maximum speed of . All members of the class were fitted for multiple working and all but two had electric train heating.
Initially all 11 were allocated to Nîmes to work services to Clermont-Ferrand.