When Bill and Ben were becoming overworked at the clay pits, the Fat Controller brought Derek to Sodor to help them out. However, as he tried to make his way up Gordon's Hill, Derek's cooling system overheated, causing him to break down. BoCo was sent to the rescue, and Derek apologized for overheating, telling BoCo about his teething troubles.
Rumours soon began to spread, and Percy informed Bill and Ben that Derek had a "toothache" after mishearing what Thomas had told him; however, Duck explained to Bill and Ben that Derek had teething troubles. The next day, Derek arrived at the clay pits and was eager to get to work, but as he pushed Bill and Ben's train up a steep hill, his cooling system overheated again and he broke down. Because of this, Bill and Ben had to pull him and the train up the hill by themselves. The Fat Controller sent Derek to the Works following the incident to have his overheating problems cured. (TVS; Double Teething Troubles)
Personality and Traits
Derek is a cheerful, charismatic and friendly diesel; even Bill and Ben admitted to liking him due to his polite nature. He tries to do his best at the jobs he is given, but his faulty cooling system makes him overheat and break down regularly. Despite his mechanical problems, Derek always retains a positive demeanour and has a passion for sorting out the trucks in their right places.
Derek is based on the British Rail Class 17 diesel engines, which were built between 1962 and 1965 by the Clayton Equipment Company and Beyer, Peacock & Co.. These diesels were designed with centre cabs and low bonnets, making visibility easy for the driver. Unfortunately, these engines were the least successful diesel engine ever employed on British Railways, as they were prone to numerous problems with the camshaft, cylinder head and other parts. Only one of the Class 17s, D8568, has been preserved, and currently resides on the Chinnor and Princes Rishborough Railway in Oxfordshire, England.
Derek is painted in the same livery as his basis. He is painted BR green with yellow warning panels, silver handrails, a black running board and red bufferbeams. He carries the British Railway logo on both sides of his cab.