The UK narration stays true to the original format from the Railway Series where the Fat Controller intended to leave Henry in the tunnel forever. In both US versions, it was said to be until Henry was ready to leave and the wall was to prevent other engines from bumping into him. The narration change was so viewers would understand the context of the storyline better so they could predict what happens later.
A previous attempt to adapt this story was made in 1953.
This is the first episode where the narrator breaks the fourth wall as he addresses the viewers in regards to the lesson of the story.
This is the first episode to feature just one location as a central part of its narrative (not counting the Pond Runby).
This episode is Henry's first speaking role, and first leading role in the television series.