According to the Government Accountability Office, the Defense Department has allocated at least $2.64 billion toward southwest border activities. That figure covers expenditures up to March 31, encompassing tasks like safeguarding Pentagon-owned border territory, erecting permanent barriers, and responding to DHS requests for support.
GAO auditors found that Pentagon financial officials employed standard budget realignment methods - sometimes without prior notice to Congress - to move money around.
An additional $336 million came from budgets designated for personnel costs - such as relocating troops and their families between assignments. The Army later returned $290 million of that amount in July 2025, according to the GAO.
The GAO report, which provides an independent examination of Pentagon fiscal practices, did not assess whether the transfers violated legal requirements. However, the scale of the diversion from facility maintenance accounts has raised concerns among some lawmakers about the long-term impact on military readiness.
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Instead, it examined the internal budgeting processes the Defense Department employed and the preliminary spending figures it reported for border operations.
The $2.64 billion figure does not include the $1 billion that Congress approved last July as part of what President Donald Trump called the One Big Beautiful Bill. Of that approved sum, the Pentagon has begun disbursing only $472 million. Moreover, the GAO's figures exclude the $1.47 billion requested for the next fiscal year beginning October 1, which lawmakers have not yet authorized.
According to the GAO, border security activities - spanning ground and air missions such as surveillance, training, aerial logistics, supply chain assistance, and intelligence analysis - accounted for more than $1.45 billion, representing over half of total border spending through March 31.
According to the GAO, the Pentagon allocated $366 million to build and maintain immigration detention facilities within the continental United States. The GAO also reported that $66 million went toward backing migrant detention efforts under Operation Southern Guard at the U.S. naval base in Guantanamo Bay, Cuba.
According to the GAO, since resuming office, Trump has overseen large-scale removal of undocumented immigrants. Early in his second term, he issued executive orders that proclaimed a national emergency along the southern border and broadened the military's involvement in immigration enforcement.
These border operations have now been running for 16 months. In March, as the operation reached its one-year mark, U.S. Northern Command - the unit responsible for the mission - told reporters that troops had completed around 22,000 "enhanced detection and monitoring missions to highlight illegal crossings" from Mexico, involving more than 20,000 service members.
The prolonged deployment and diversion of maintenance funds have sparked debate in Congress about whether the military's core readiness is being compromised.
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