TYPICAL WATER WHEELS IN THE LATE 18TH AND EARLY 19TH CENTURIES were constructed of wood. Radial spokes commonly connected a pair of wheel rims to a large oak shaft. Between the wheel rims were fitted either paddles or buckets – partitions set into slots in the wheel rims. A stream of water, called the "head," was directed from above the wheel either against the paddles or into the buckets. The force of this impact against the paddles or the weight of the water in the buckets – or a combination of both – kept the wheel in motion. The rotating wheel shaft, through gearing, transferred this drive to the mill's machinery. The main difference in detail between one water wheel and another was its diameter, breadth, and direction of rotation. Overshot wheels, for instance, carried the water over their top, while undershot, backshot, and breast wheels turned in the opposite direction.

At the Harpers Ferry Armory, breast wheels were popular in the early 1800s. These wheels were fitted with deep buckets, or troughs, and were turned both by the weight of the water carried in the buckets and by the impulse of the water striking the wheel. An apron, or breast, fitted tightly to these wheels helped prevent water from leaving the buckets prematurely, thereby increasing the effect of gravity upon the wheel. Since water was admitted to the upstream side of the wheel near the middle, wheel diameters much greater than the height of the fall could be used. This gave millwrights considerable flexibility in adjusting the speed of rotation to suit the machinery being driven. And since the breast wheel rotated with, instead of against, the flow of water in the tailrace, the damaging effect of "backwater" caused by occasional high water was reduced. In about 1801, five breast-type water wheels operated at the Harpers Ferry Armory. [Learn more about the Harpers Ferry Armory].

Improvements to the water works at the Harpers Ferry Armory in the 1840s, and new fabrication techniques – including the use of strong and durable wrought iron – enabled the government to build larger, more powerful water wheels. Two 15-foot diameter overshot wheels – one built entirely of iron – and a large backshot water wheel 15 feet in diameter by 10 feet wide were put into operation in about 1845. These three water wheels powered arms-making machinery right up until the Civil War.

Before the advent of iron, wooden water wheels required constant maintenance. In 1825, the superintendent of the Springfield Armory reported that wooden water wheels would not last more than eight years without considerable repairs, adding that "with constant expense they may be kept along with frequent interruptions two or three years longer."

Problems with the water wheels at Harpers Ferry were typical of the problems faced by 19th century millwrights everywhere. In 1820, Armory superintendent James Stubblefield informed the Ordnance Department that in "the month of Sept our water wheel in the polishing Mill gave way & I had then to put in a new wheel which caused a considerable delay…." When Chief of Ordnance George Bomford requested funds from Congress for three new water wheels in 1833, he wrote:

"The water-wheels and machinery (generally) are so much worn and decayed as to require very frequent repairs… the loss of time sustained by the workmen for the want of the necessary power to propel the machinery causes the cost in fabricating some of the component parts of the musket to be much greater..."

As late as 1850, problems with water wheels still hampered Armory operations. On October 25, Armory Superintendent John Symington informed the Ordnance Department:

"The wheel which drives the blast of all these fires at the Musket factory, broke down. It was one of those miserable affairs, having cast iron toothed segments bolted on the arms near to the outer rim. These teeth together with the teeth of the spur wheel, on the shaft driving the blast cylinder, were a good deal worn, but it was confidently hoped they would hold out until we should be in our new shop (in from three to four months). "The breaking of one tooth however caused such a jar, that others soon were broken around the spur wheel and segments. A new spur wheel is being cast and a pattern being made for the segments, and the repairs will be prosecuted night and day till completed."

Freezing temperatures also posed operational problems for millwrights. Because water wheels generated so much dampness, they were often located outside of the mills and factories they served. At the Harpers Ferry Armory, all of the original breast wheels were placed outdoors, with some predictable consequences. In 1817, Superintendent Stubblefied advised the Ordnance Department that, "Owing to extreme cold weather which has stopped our water works for the last four weeks, we have not been able to complete the Rifle & Musket." The story was the same in 1821, when Stubblefield wrote that the "month of January was so extremely cold that our water wheels were frozen-up nearly all the month…." These problems were rectified in 1822 when three sheds were erected over the principal water wheels and furnished with stoves for heat.