Built in 1994 and used by the contractors who re-laid the entire line in conjunction with the I.RI.S. all-island sewage project, this locomotive was originally built to three foot gauge but subsequently re-gauged to two foot and used in conjunction with the Jubilee Line extention of the London Underground, then gauged back for use on the island.  Bought from the contractors upon completion of the work and named Ailsa in honour of the man who did so much to keep the railway alive in the late 1960s. It was stated at the time of purchase that the loco would receive a spring green livery (as it was standard livery at the time of the Marquis’ ownership and operation) but it remains in plain white livery to date, only receiving a fleet number on the rear cab plate only.