The 601 class locos were designed as light shunters for use in freight yards. The later 611 class was identical to the 601 class except they had added vacuum brakes.
The 601 & 611 class locos were originally designated the G class. The 601 class locos were delivered in 1957, the 611s were delivered in 1962, the 611 class proved useful working single coach branch line trains.
The G class locos were built by deutz, they were fitted with a Deutz V8L 714 engine capable of 120 b.h.p. They were capable of 25 m.p.h and were of a B wheel arrangement.
The locomotives saw little use in CIÉ ownership as the E class locos had far more pulling power, it was when they were sold on they really showed what they could do. In 1977 a few locomotives were sold to Irish Sugar where they shunted small loads of sugar beet and empty wagons for mainline locomotives to collect. Later, 3 of these locomotives plus another from CIÉ were sold into preservation with the Irish Traction Group where rather than being put in a museum or used on railtours, they were loaned to the Downpatrick & County Down heritage railway where they perform shunting and maintenance trains duties, as well as occasionally operating public passenger trains.