FIRST ON FOX — The Pentagon is preparing U.S. military bases to keep operating for at least 90 days without outside support as it prepares for the possibility of a major war that could cripple power grids, disrupt supply chains and threaten critical infrastructure on American soil.

The new requirement is part of FORTRESS, a broader military initiative aimed at ensuring American forces can continue fighting even if the civilian systems they depend on are disrupted, according to documents reviewed by Fox News Digital.

"We don't want to rely on standard civilian municipal infrastructure to run our national defense. We just simply can't. It's an intolerable risk," Pentagon chief spokesperson Sean Parnell told Fox News Digital.

The Pentagon is also laying the groundwork for civilian factories to shift to defense production during a crisis, while preparing alternative supply chains and strategic reserves to keep weapons, fuel and other essential materials flowing.

"Power is combat now. Without electricity, you lose communications, water, logistics, assembly lines and just basic military command structures," Parnell, who led the FORTRESS initiative, said.

Under FORTRESS, every major military installation in the continental United States would be expected to sustain essential operations independently for at least 90 days, including access to electricity, water, fuel and communications.

President Trump's deployment of 4,000 members of the California National Guard to the Los Angeles area last year was an unlawful abuse of his authority, according to a federal appeals court ruling on Friday.

The court's 2-1 decision by a three-judge panel of the U.S. 9th Circuit Court of Appeals follows precedent set by the U.S. Supreme Court in December, holding that Trump's federalization of the Illinois National Guard was illegal.

California Gov. Gavin Newsom, a Democrat, issued an immediate statement celebrating the court ruling against Trump, saying the president had no authority to intervene by using National Guard troops.

"Today is a crucial day for the rule of law, upholding the Constitution and defending democracy," Newsom said. "Yet another court has issued a complete rejection of Donald Trump's illegal, authoritarian takeover of our state's National Guard.

"California fought back against this potential power grab and, in doing so, created essential legal precedent that not only protects Californians but all Americans. California continues to stand as a first line of defense against Donald Trump's authoritarianism."