Henry's Tunnel (T&F)/Behind the Scenes

Background Information
Henry's Tunnel is a fictional tunnel near Ballahoo on the Island of Sodor created by the Rev. W. Awdry.

Henry's Tunnel first appeared in the first series episode Thomas and Gordon, which first aired in 1984. Its last appearance was in the twenty-second series episode Hunt the Truck, which was released in 2018.

Gauge 1 sets
Henry's Tunnel was first built for the first series of the television series.

The tunnel and its surroundings have undergone numerous changes throughout the television series:
 * Series 1:
 * One tunnel bore had two tracks and the other bore had one track.
 * Series 4:
 * The design of the tunnel changes slightly.
 * The numerous switch tracks and the siding disappeared.
 * The tunnel entrance brickwork becomes a darker colour.
 * Thomas and the Magic Railroad only:
 * The design of the tunnel changes again.
 * Both bores had two tracks and there was track on top.
 * The tunnel is slightly raised to accommodate for Pinchy’s height on Diesel 10 and would remain this way onwards.
 * Series 7:
 * A signal box and water tower had appeared and disappeared at the portal.
 * Each bore had one track, like its Railway Series counterpart.
 * Series 8:
 * Both bores had two tracks again.

Close-up set
A close-up model of a small portion of Henry's Tunnel was built to be used for scenes involving the close-up scale figures.

CGI set
In 2009, the series introduced Computer-Generated Imagery (CGI) as a replacement for the show's long-standing live-action models. Henry's Tunnel was recreated from scratch in CGI by Nitrogen Studios. The model was "hand-sculpted" in Maya, a 3D animation and modelling software.

According to Greg Tiernan, the CGI models are subjected to many rounds of review before they are submitted to HiT Entertainment for final input and approval.

Henry's Tunnel has had modifications throughout the CGI era. These include:
 * Series 13:
 * The tunnel seemed to get shorter since its other end was visible.
 * The tracks became slightly curved on one end of the tunnel.
 * Blue Mountain Mystery only:
 * The tunnel was seen in a flashback and it had one track in each bore.
 * The additional elevation of the tunnel that had been gained during Thomas and the Magic Railroad was removed.
 * The Adventure Begins:
 * Two switch tracks were added in front of the signal box.
 * The Great Race only:
 * The track on top of the tunnel reappeared.