The first David Brown ploughs were designated or known as ‘Principle Unit’ PU ploughs. David Brown started producing them around 1938 and were initially trailed ploughs of either 2 or 3 furrow 8 or 10 inch general purpose bodies and the land/depth wheel was an iron spoked wheel. When the option of a hydraulic ‘power lift’ was offered for the VAK1 the same ploughs were produced but modified with an adjustable cross-shaft operated from a link connected to the left lift arm of the tractor and via a lug on the cross-shaft to control the width of the furrow. The early hydraulic PU ploughs also had the spoked land wheel but later were offered with a pressed steel one as an option. There was another option of a rubber tyred wheel. There were 5 ploughs in the PU series. PU1 was a 10 inch general purpose adjustable to 11 and 12 inch and available in 2 furrow form. The PU2 was a 12 inch semi-digger, adjustable to 10 or 11 inch. The PU3 was a single furrow deep-digger plough with a 16 inch furrow. The PU4 was a 3 furrow general purpose plough with 10 inch furrows adjustable to 8 and 9 inch. The PU5 was a 2 furrow 10 inch plough adjustable to 8 and 9 inch. All these ploughs were fitted with 15 inch coulters as standard but various options of shares were available for different soil conditions and types and longer mouldboards for ley (grassland or turf) wer offered as an option. Th PU plough series were produced up until around 1950-51 when the ‘A’ series were introduced.