The Sodor and Mainland Railway originally attempted to cut a tunnel through the Ballahoo Ridge. However, it collapsed during construction, resulting in the railway only running trains between Ballahoo and Kirk Ronan.
After its foundation in 1915, the North Western Railway constructed its own tunnel in order to reach Vicarstown. The NWR was built as a strategic railway in a time of emergency. Speed and cheapness of construction were paramount, so a single line bore only was cut, with the Up and Down lines being gauntletted. While work was in progress, a section in the centre collapsed, leaving two tunnels (the Western - 1 mile, and the Eastern, or Henry’s - 450 yards).
The tunnel gained its nickname in 1922 after Henry refused to come out, claiming that the rain would spoil his "lovely green paint with red stripes", and was subsequently bricked up after three failed attempts to get him out. A second bore was cut alongside to provide a double line and Henry was eventually let out sometime in 1923 to help with the express. In 2011, the tunnel collapsed but was repaired in time for the unveiling of the Thin Clergyman's bust at Tidmouth.
In Wilbert Awdry's original drawing, the tunnel had one track instead of two.
In the first series of the TV Series, the tunnel seems to be just east of Knapford and west of Crosby, standing in for the Crosby Tunnel, instead of west of Vicarstown, as it was in the Railway Series. The tunnel is in the correct location in the CGI series.
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