<div class="css-s99gbd StoryBodyCompanionColumn" data-testid="companionColumn-0"><div class="css-53u6y8"><p class="css-at9mc1 evys1bk0">Defense Secretary Pete Hegseth ordered the shuttering of the Office of Net Assessment, a small, often secretive and sometimes opaque office that for more than 50 years has helped the Pentagon’s most senior leaders think about the future of war.</p><p class="css-at9mc1 evys1bk0">The office costs about $10 million to $20 million a year — a fraction of the Pentagon’s $850 billion annual budget — but its work and staff of about a dozen civilians and military officers has often had an outsize impact on how the Pentagon prepares for possible conflicts.</p><p class="css-at9mc1 evys1bk0">In a short note posted on Thursday, the Pentagon spokesman Sean Parnell suggested that the office would be restructured and then reopened with a new focus on the country’s most “pressing national security challenges.” He did not explain how the office’s new mission would differ from its previous approach.</p><p class="css-at9mc1 evys1bk0">For most of its history, the Office of Net Assessment was run by Andy Marshall, its founder, who pioneered an innovative and somewhat mysterious approach to comparing the strength of U.S. forces with that of its potential enemies. The office also developed inventive ways of fighting adversaries. Jim Baker, a retired Air Force colonel, succeeded Mr. Marshall in 2015.</p></div><aside aria-label="companion column" class="css-ew4tgv"></aside></div><div data-testid="Dropzone-1"></div><div class="css-s99gbd StoryBodyCompanionColumn" data-testid="companionColumn-1"><div class="css-53u6y8"><p class="css-at9mc1 evys1bk0">The office’s influence often depended on the defense secretary’s priorities and personal relationship with its director. In the early 2000s, Defense Secretary Donald Rumsfeld relied heavily on Mr. Marshall to develop ways of fighting that relied on speed, precision munitions and rapidly improving surveillance capabilities to quickly defeat adversaries.</p><p class="css-at9mc1 evys1bk0">More recently, the office focused on developing concepts for a possible war with China. 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