No. 18 was built for the Jubilee line extension of the London Underground in 1994 and used by the contractors who re-laid approximately two-thirds of the Port Erin line in conjunction with the IRIS project (a sewerage scheme which saw a main pipeline being laid beneath the railway in 2000-2002, resulting in shuttle services being operated). The locomotive was bought from the contractors upon completion of the work and named "Ailsa" in honour of Archibald Kennedy, 7th Marquess of Ailsa, who had greatly contributed to the railway in the late 1960s.
