The introduction of the lightweight Lycoming T-53 shaft-turbine engine provided Bell designers with an excellent solution to a vexing industry problem: How to gain increased lifting power without developing a massive multi-engine aircraft. The earlier Sikorsky H-34 Chocktaw, a helicopter largely succeeded by the
H-1 Iroquois, was powered by a 1525 HP Wright R-1820 piston engine that weighed approx. 1400 lb. The UH-1D Iroquois was powered by an 1100 HP Lycoming T-53-L-11 shaft turbine that weighed approx. 496 lb.

With this significant power to weight advantage, Bell was able to produce a family of helicopters that grew in capability as the powerplant's shaft horsepower (SHP) grew. The manufacturer was able to respond to the increasing operational needs of the US military, in particular, the demands for increased support from the US Army’s helicopter units. Larger, more capable versions of the H-1 “Huey” series, such as the UH-1D quickly followed the UH-1A,B & C into production.

The troop-carrying ability of the enlarged UH-1D was increased to 12, up 33% from the earlier versions. Production of the UH-1D totaled 2008, many of which were later converted to UH-1H standard with the 1400 SHP T-53-L-13 engine.

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