RENFE Class 333
The RENFE Series 333 are high power six-axle diesel-electric locomotives built in the 1970s; at the time of their introduction they were the most powerful non-electric locomotives in Spain.
After three decades of service the class were rebuilt incorporating Alstom's newer technology, and thus extending their life - these rebuilt machines were given the sub-class names 333.3 and 333.4
Background
In the early 1970s, RENFE was looking for a new, diesel-engined locomotive capable of both hauling express trains and high-tonnage heavy freight trains nationwide at a steady speed of 120 km/h (75 mph).
At the time, RENFE's dieselization program, with the 316 and 318 series CC locomotives, later followed by the more numerous 319 and 321, had displaced steam powered traction and were responsible for much of the work requiring higher-powered locomotives.
The Class 319, produced in collaboration between Macosa and General Motors, had shown good performance, which influenced the decision to choose a locomotive of the General Motors type GT 26, (3,300 hp (2,500 kW)).