Mr Trump received a boost when 88 former military leaders expressed their support for him
Donald Trump would give his generals 30 days to devise a plan to defeat Islamic State.
Mr Trump, who is running against Hillary Clinton in November's election, told a rally in North Carolina: "We are going to convey my top generals and give them a simple instruction.
"They will have 30 days to submit to the Oval Office a plan for soundly and quickly defeating ISIS. We have no choice."
The Republican nominee is expected to announce a plan to end budget cuts for the military and instead increase spending on the armed forces if he is installed at the White House.
On Tuesday Mr Trump received a boost when 88 former military leaders expressed their support for him in an open letter.
The group, which included retired generals and admirals, said the 70-year-old had the temperament to be commander-in-chief.
They said they trusted him more than Democratic nominee Hillary Clinton, who they said had been deeply involved in "the hollowing out of our military and the burgeoning threats facing our country around the world".
Mr Trump called their support "a great honour".
But Mrs Clinton's running mate, Democratic vice presidential candidate Tim Kaine, has accused Mr Trump of disrespecting the US military.
He said Mr Trump was woefully underprepared and temperamentally unfit for the role of commander in chief, and had no idea how to combat IS.
Mrs Clinton's team has released a campaign ad featuring veterans being critical of Mr Trump.
The Presidential contenders are to take part separately in a national security forum on Wednesday.
Hosted by the Iraq and Afghanistan Veterans of America, it will include questions from an audience of military service personnel.