What is British Rail Class 13?
{{Infobox Locomotive |name = British Rail Class 13 |powertype = Diesel-electric |image = |caption = 13001 at [[Tinsley TMD]] on [[14 April]] [[1984]] |roadnumber = D4500–D4502, later 13001–13003 |builder = [[British Railways]]’ [[Darlington Works]] (builder and rebuilder) |builddate = 1965 (rebuilt) |totalproduction = 3 |gauge = {{RailGauge|ussg|lk=on|al=on}} |primemover = [[English Electric diesel engines|English Electric 6KT]], 2 off |transmission = DC generators, DC traction motors, double reduction gearing |tractionmotors = EE, four off |whytetype = 0-6-0+0-6-0 |uicclass = C+C |wheeldiameter = {{convert|4|ft|6|in|m|3|abbr=on}} |minimumcurve = |trainbrakes = Vacuum |locobrakeforce = {{convert|37|LTf|sigfig=2|lk=on}} |wheelbase = {{convert|42|ft|1+1/2|in|m|2|abbr=on}} |length = {{convert|60|ft|1|in|m|2|abbr=on}} |width = {{convert|8|ft|6|in|m|2|abbr=on}} |height = {{convert|12|ft|8+1/2|in|m|2|abbr=on}} |locoweight = {{convert|120|LT|sigfig=3|lk=on}} |topspeed = {{convert|20|mph|km/h|abbr=on|lk=on}} |poweroutput = ''Engine:'' {{convert|350|hp|0|abbr=on}} × 2 |tractiveeffort = ''Maximum:'' {{convert|70000|lbf|kN|1|abbr=on|lk=on}} |fuelcap = {{convert|1336|impgal|abbr=on|lk=on}} |trainheating = None |multipleworking = Not fitted (except control of slave by master) |axleloadclass = [[Route availability|RA]] 8 |railroad = [[British Railways]] |retiredate = 1983–1986 }} The [[British Rail]] '''Class 13''' was formed in 1965. The [[Tinsley Marshalling Yard]] needed more powerful shunters to move vehicles around. This was provided by permanently coupling together two [[British Rail Class 08|Class 08]] shunters as a ‘master and slave’ (or ‘[[cow-calf|cow and calf]]’) unit. The second of the two units had its cab taken off. Both units were ballasted to improve traction. At first the units were coupled cab-to-cab but it was easier to couple Master nose to Slave cab. The thinking behind adopting this dual locomotive design is that a larger, rigid locomotive could not be used due to the risk of