Dozens of retired generals and admirals on Tuesday announced their opposition to President Trump's tweeted ban on transgender military service and questioned his reasons for the move.

The 56 former senior officers, who signed a joint statement released by the Palm Center advocacy group, said the ban would rob the armed services of talent and would force the return of a "Don't Ask, Don't Tell" kind of policy for transgender troops now serving.

"Patriotic transgender Americans who are serving — and who want to serve — must not be dismissed, deprived of medically necessary health care or forced to compromise their integrity or hide their identity," the statement said.

Trump's claims that transgender service is too costly and disruptive are "without merit," argued the group of retired officers, which included Marine Corps Gen. John Allen, who oversaw U.S. security operations in Afghanistan and gave a rousing speech at the Democratic National Convention last summer.

The officers cited a Rand Corp. study last year that found healthcare for transgender troops would be about $8.4 million annually, a fraction of overall military costs, and that 18 other nations allow open service.

Trump announced a complete ban on transgender service via Twitter last week. The Pentagon has said it is continuing with existing personnel policies that allow troops to serve openly until it receives guidance from the White House.

"After consultation with my Generals and military experts, please be advised that the United States Government will not accept or allow transgender individuals to serve in any capacity in the U.S. Military," Trump wrote. "Our military must be focused on decisive and overwhelming victory and cannot be burdened with the tremendous medical costs and disruption that transgender in the military would entail."

Here are the retired officers who signed the letter: