This half hour special had been in development for well over a year. It was always intended to introduce a truly villainous character at some point, and it came in the shape of English Electric's finest: the prototype DELTIC diesel. I had bought one as a birthday present for my father that year, and there were no objections to using it in the series as a villainous engine of sorts.

Day of the Deltic was originally intended to be the seventeenth episode of the series, behind two titles named Fowler's Ghost and Great Scott!. It was only when the scripts were analysed that it was seen that the Deltic episode would fit better into the series line up as the next episode after the fourteenth episode, Silent Night.

Development of the set continued from Episode 14 straight onto Episode 15. A new siding was added, the length of the yard enlarged (the carriage works being the main beneficiary), and lots of set work to make it look like a steam era yard were added: disused spoked wheels, two coal heaps, ash and clinker between the shed's running lines; even a scrappy traction engine were added to complete the effect of the yard.

There have been questions as to the year of the episode: it is in fact 1959. The reason for this date is simple. Stephen the Holden B12 states that he is "the last of his kind" - number 61572 was indeed the last Holden B12 left by 1959. This means that there is roughly four years between Gronk's first appearance at Copley Hill in episode eleven, and this episode, number fifteen. Therefore it is say to assume that the liveries carried by Allen and Sir Ralph are both livery errors (that is to say, they should be painted in Brunswick green and not Express Passenger blue by the time of the episode).

It was too costly at the time to buy and convert two new models for Allen and Sir Ralph, and it was also too time consuming to repaint the two (near-expired mechanically) current models. There was a suggestion made to replace their parts in the script with Arthur and Scott (by this time repainted into Brunswick, although the blue model was eventually used instead of the new green one), however neither of the arguments involving the A1 and A4 pacific would have had a much resonance had it come from Arthur and Scott instead.

The one notable addition to the models was the use of a Seuthe smoke generator in the Stephen model, which led to some memorable night time shots. Further, a new smoke generating machine was used for the shed scenes, and finally, for the wind shots, a special aerosol was bought to mimic these effects. It was due to the small amount of smoke seen in the series so far, that prompted me to start buying up seuthe generators and fixing them into the engines. At this time, Stephen was the only one fitted. At the current time of writing, the only models which have not been fitted are those models with split chassis mechanisms (Herbert, Nigel and Tavish) as there is little space in the model to fit no.22s which I use as a standard.

There is one final factor to consider, plotwise, in this episode. If the year is 1959, then this failure by DELTIC on the mainline is NOT the catastrophic engine event which ended the real engine's working life in 1961. This means that while the Day of the Deltic might be over, the presence of DELTIC himself is not fully realised. It shall return in a future episode...