Mr Trump has asked for $30 billion of the military money immediately, in the form of a supplemental request on the current budget.
The president has offered few specifics, but here are some key reasons he says the Pentagon needs the money:
The additional funding "provides the resources" needed to increase the tempo of the war against the ISIS.
The United States has spent about $12 billion since fall 2014 bombing ISIS targets in Iraq and Syria, but Mr Trump wants to increase the number of air strikes and possibly put more US forces on the ground.
This year's supplemental budget request calls for an immediate additional $2 billion for the campaign.
A constant refrain from military leaders has been a lack of "readiness" across the services and generals have warned lawmakers that aging equipment, chronic underfunding and understaffing have impacted how the military can effectively respond to crises.
Mr Trump's budget states it would ensure America is "the best led, best equipped, and most ready force in the world."
'Rebuilding' the military
Mr Trump has promised a "great rebuilding" of the US military and his budget reiterates that pledge, again without specifics. Mr Trump particularly wants to swell the Army's ranks and the budget "begins to rebuild the US armed forces by addressing pressing shortfalls, such as insufficient stocks of critical munitions, personnel gaps, deferred maintenance and modernization, cyber vulnerabilities, and degraded facilities."
The budget says America needs to spend more on defense in the air, land and sea -- and also in cyberspace.
Mr Trump in January signed an executive order to begin increasing the size of the US military, promising new aircraft, naval ships and more resources for the Pentagon.
He offered few specifics but has said he envisioned a naval fleet of 350 vessels, up from the Navy's current 274 and more than its 310-vessel target.
The budget "reflects a down payment" on that pledge.
Despite the apparent bonanza, hawkish Republicans say Mr Trump's military budget doesn't go far enough, and some Democrats are horrified the president wants to fund America's war machine by deep cuts to other programs and agencies.
The result is that the proposed budget will likely look very different from the one that passes.
"It is clear to virtually everyone that we have cut our military too much and that it has suffered enormous damage," Republican Congressman Mac Thornberry said.
"Unfortunately, the administration's budget request is not enough to repair that damage and to rebuild the military as the president has discussed."
Mr Trump also would struggle to get this year's supplemental request passed, given the fiscal year is half done and Congress would need to raise spending caps.