The Pentagon warned of pandemic danger in mid January. Gen Mark Milley told reporters on March 23 the Pentagon became concerned about deadly nature of the pandemic in mid-January, and published an execute order on Feb 1 to take its Global Pandemic Operation Plan "off the shelf."

According to Gen Mark Milley, Chairman of the Joint Chiefs, in an on the record phone briefing 3/23 when asked when the US military anticipated coronavirus could pose a pandemic like threat to the continental US…Gen Milley said the military became concerned in mid-January...

and published an "EXORD," or execute order on February 1 based on the US military's Global Pandemic Operation Plan, which was already "on the shelf." The Pentagon could not execute the order without being ordered to do so by the Defense Secretary or President ...

but US military on Feb 1 published the EXORD as a way of leaning in and anticipating being asked to help civilian authorities like FEMA, reporters were told during the March 23 phone brief. US military began making anticipatory preps, setting up a crisis management team on Feb 1.

May 5th
Defense Sec Mark Esper: "We issued our first force health protection guidance on 30 January and have released updated guidance at least eight times since then." https://www.defense.gov/Newsroom/Transcripts/Transcript/Article/2178112/defense-department-senior-leaders-brief-reporters-on-dod-efforts-regarding-covi/