The main considerations were the rising cost of coal against diesel oil and the weight of the trains causing wear and tear on the track.

In looking to the dieselisation of their system the Ulster Transport Authority (UTA) made early inroads with small, lightweight diesel units, based on those built for the Great Western Railway in England, using the same manufacturers to supply parts and undertaking construction in their own workshops.

In August 1951 UTA's York Road works outshopped two new power cars which, following on the first diesel acquisitions, were numbered 6 and 7.

To increase capacity the unit ran with coach 279, as a centre trailer car, which was converted to work with this set.

At the same time, (1950/1), AEC were also responsible for power cars supplied to the GNR(I) and on the division of stock of that company in 1958 ten of these entered the UTA lists.