For about four years, senior U.S. military officers have feared that the financial costs of developing interceptors to destroy incoming ballistic missiles could jeopardize a domestic missile shield. They’ve sought what’s called “left of launch” options to disable adversary missiles before they leave the launchpad. And they’ve intimated that a more cost-effective approach is to develop digital weapons to corrupt or disable launch controls, guidance systems or aspects of the missile supply chain.

The unclassified document from May 2017, acquired by The Daily Beast, asserts that “pre-conflict left of launch operations” would be legal against an “imminent missile attack,” without defining “imminent.” It explicitly cites “non-kinetic options” for destroying missiles that would fall short of a “use of force” under the United Nations charter.

Missile experts who reviewed the document understood it as representing what appears to be the first official confirmation that the U.S. reserves the right to infect adversary missile networks with disabling malware. It appears to confirm a March 2017 New York Times report that the Pentagon was looking to add digital-network assaults to its antiballistic missile arsenal.