The Little Western was originally intended to reach Harwick; however, by the time Arlesburgh was reached in 1916, it was found there was no longer need for further extension and it was dropped. In the 1940s, a rail link between Arlesburgh and Harwick was again proposed, but yet again deemed unnecessary, for it was found that Sodor Roadways could provide adequate transport both for stores and personnel.
When the initial line was being constructed, the ground became unstable. Engineers declared the site unsafe and the track had to be re-routed. Soon after, Thomas had a severe accident, causing the unstable ground to completely give way. This giant opening revealed a long-lost hidden cavern, known as "Calles Cavern".
Later, the construction of the Harwick Branch Line resumed and the new re-routed line was finally finished.