Demand for military goods is highly volatile and had surged in April, so the sharp drop in May wasn't a surprise and was dismissed by many economists.
"Monthly defense orders are so regularly irregular that they do not matter, given their tendency to promptly reverse," said Michael Montgomery, an economist at IHS Global Insight.
Factories reported higher demand for steel and other metals, computers, and autos. Durable goods are items expected to last at least three years.
The figures come as a separate report showed that the U.S. economy contracted sharply in the first three months of the year, largely because of bad weather. The economy shrank 2.9 percent at an annual rate in the first quarter, the worst showing since the first quarter of 2009, in the depths of the Great Recession.
But most economists expect growth has resumed in the current quarter, partly because of rising manufacturing output. Most analysts expect the economy will expand by 3.5 percent in the April-June quarter.
Factory production rose at a steady pace last month, according to the Federal Reserve, as manufacturers cranked out more cars, machinery, furniture, computers and appliances. More output of those goods points to rising demand from consumers and businesses.
And auto sales reached a nine-year high in May as Americans ramped up purchases of SUVs and pickup trucks.
A survey by the Institute for Supply Management, a trade group of purchasing managers, found that manufacturing expanded faster in May than in April. A measure of new orders also rose, pointing to further growth in output in the coming months.
Manufacturers are hiring more to keep up with demand. Factories added 10,000 positions in May, and the average work week for manufacturing employees grew.