The letter, published on Thursday, argues that the current president has demonstrated that he is “not equal to the enormous responsibilities of his office.”
It also says that Biden has "the experience and wisdom necessary to navigate America through a painful time."
“We are former public servants who have devoted our careers, and in many cases risked our lives, for the United States. We are generals, admirals, senior non-commissioned officers, ambassadors, and senior civilian national security leaders," the letter reads.
"We are Republicans, Democrats, and Independents. We love our country. Unfortunately, we also fear for it.”
Among the signatories was one of Trump’s most senior military advisers, retired general Paul Selva, who served as vice chairman of the Joint Chiefs of Staff until July 2019.
The letter was released the month after a controversial article in the US magazine the Atlantic claimed that Trump had called Americans who died in war “losers” and “suckers.”
Trump has denied the report and said that he supports US service members.