The surprising decline reflects uncertainty over the global economy that is likely to be magnified by the U.K.'s "Brexit" vote.
But orders for non-defense capital goods (excluding aircraft) fell 0.8%, said the Commerce Department.
Declines in U.S. goods were offset by an uptick in the labor market.
The 5.1% drop for the month and the 3.5% decline for all of 2015 has economists worried about a pullback in capital investment.
"Core" capital goods orders, a key gauge of business spending plans, rose last month.
What message are economic data sending? It's hard to tell.
