The British Rail Class 73 is a British model of electro-diesel locomotive. The type is unusual in that it can operate from the Southern Region’s 650/750 V DC third-rail or an on-board diesel engine to allow it to operate on non-electrified routes. This makes it very versatile, although the diesel engine produces less power than is available from the third-rail supply so the locomotives rarely stray from the former Southern Region of British Rail. Following the withdrawal and scrapping of the more powerful Class 74 electro-diesels in 1977, the Class 73 is now unique on the British railway network. Ten locomotives have been scrapped.