The US Army will "temporarily" increase its size by 22,000 soldiers for the next three years, Defence Secretary Robert Gates has announced.
The additional troops are intended to ease the strain of the United State's deployments in Iraq and Afghanistan, Mr Gates said.
The extra manpower will raise the total number of active American soldiers to 569,000.
Mr Gates's defence budget, unveiled in April, set aside $US11 billion to fund increases in military personnel.
"The army faces a period where its ability to deploy combat brigades at acceptable fill rates is at risk," Mr Gates said.
"This is a temporary challenge which will peak in the coming year and abate over the course of the next three years."
Mr Gates's budget plans have faced fierce opposition from US lawmakers, who oppose his proposal to cease production of the F-22 fighter jet.
The defence secretary argued that the F-22, which was designed in the 1980s, was no longer strategically useful.