No.16 Mannin was the last locomotive to be supplied by Beyer, Peacock & Co. and was by far the most powerful locomotive on the railway. Ideal for the heavy south boat trains, a job which had previously taken two locomotives either double-headed or banked. It was considerably larger than previous orders with a 3'6" diameter boiler, large tanks with a capacity of 520 gallons each, higher pressure and 12" bore cylinders. It was also the only locomotive to be fitted with vacuum ejectors from new and steam sanding equipment. Spending the majority of its working life on the south line it saw little use outside the main holiday season Never re-boilered it was relegated to lighter duties on the Peel Line latterly, with reduced pressure and lasting until 1964 with it was withdrawn and stored.
Repainted into the new Spring Green livery and displayed at St John's in 1967 and 1967, on closure of the Peel and Ramsey lines it was and later on show at Douglas Stations until entering the then-new railway museum in 1975 when it was repainted into the post-war Indian Red livery without lining detail, funded by the Association. Only removed from the museum once when the exhibition hall was rebuilt 1998/1999, it was at this time that the lining was finally applied. Plinthed on an isolated section of track on return to the museum, and turned for visuall impact, it was removed again in 2019 when it was announced that it had been selected for restoration to working order, the initial plan being for an unveiling as part of the 150th anniversary celebrations in 2023. In the event this did not occur though the boiler was taken to the Seven Valley Railway and the rest of the locomotive moved to off-site contractors to play with. To date there has been no final decision on a return to service though many in the enthusiast fraternity are keen for this.