The U1, numbered 2395, was initially allocated to Barnsley shed but due to the restricted layout there was transferred to Mexborough on 17 October 1925. The locomotive was used to bank heavy trains up the Worsborough Bank, making up to 18 return trips each day; a typical train consisted of an LNER Class O4 locomotive with 60+ loaded coal wagons then an assisting engine at the rear, usually another O4 or an Ex-GCR Class 1B, and finally the U1. The U1 was attached at Wentworth Junction at the bottom of the bank, and pushed for the to West Silkstone Junction at the top where it would be detached, while the assisting engine would normally continue as far as Dunford Bridge. Prior to the introduction of the U1 a further two O4 locos would have been used for this work although the additional effort required to operate such a large locomotive as the U1 was not appreciated by the crew; "Twice the work but the same sodding pay" summing up their opinion.