The O&K CSÉT Shunting Locomotives were a class of nine small Irish steam locomotives built in Berlin, Germany, by Orenstein & Koppel for shunting wagons of sugar beet at the three Irish Sugar Company (Comlucht Siúcre Éireann) factories in Mallow, Thurles and Tuam.

There was no official class designation, but in preservation they have gained the nicknames Sugarpuffs, due to their small size and careers in the sugar industry, and O&Ks, which is the acronym of their manufacturer.

The locomotives were easy to recognise in Ireland thanks to their diminutive size and European characteristics - which included a sandbox on top of the boiler, and a funnel-shaped chimney which allowed for the potential fitting of a spark arrestor for wood-burning.

CIÉ offered a disused bus garage at the former MGWR Broadstone station to the locomotives as a replacement home, but this necessitated transport by lorry through Dublin.

2 was sold to a scrap merchant, where she languished for several years as her new owners, reluctant to cut her up, tried to find a buyer.

1 & 3 were moved by road from Broadstone to the former site of Ballynahinch Junction railway station, and it was here that their owner finally realised that the gauge in Ireland was substantially wider than that of Great Britain, thus rendering the locomotives useless to him.

3's boiler was sent to Whitehead for overhaul in January 2016,[6] returning in early 2017, and on Thursday 24 August the locomotive was reassembled so that testing could start.

3 was steamed in her frames for the first time post-overhaul on 19 May 2018, and passed her final boiler inspection on 12 November 2018,[7] releasing her into traffic.