Numbers 4301 to 4316 of the Norte were 16 three-cylinder 4-8-0 locomotives, called “Mastodontes” in Spain. Although ordered from Babcock & Wilcox, this company contracted their construction to the Yorkshire Engine Company. They had a Belpaire firebox with a large grate that was pitched down steeply. To negotiate the curves in the Spanish mountains, the fourth driving axle had 10 mm of lateral play, while the second one had thinner flanges. One design feature that was not well received were separate regulators for saturated and superheated steam, patented by Babcock & Wilcox, as these tended to seize up when running under full steam. Additionally, the consumption was higher than that of two-cylinder locomotives and they could not be used on some lines due to their high axle load. Yet, they were only withdrawn between 1964 and 1966.