“Don’t Ask, Don’t Tell,” the policy barring gay people from serving openly in the military, should be history on Sept. 20. That’s when President Obama’s repeal of the law is scheduled to go into effect — and when a documentary on the controversial policy, The Strange History of Don’t Ask, Don’t Tell, premieres on HBO. The film, by directors Fenton Bailey and Randy Barbato (The Eyes of Tammy Faye), tracks the 17 years it took to overturn the policy — starting with President Clinton’s signature signing into law in 1993 and ending with Obama’s repeal in Dec. 2010. Along the way, it tells the history of gay people in the military as well as the stories of some of the estimated 60,000 gay and lesbian Americans currently on active duty. HBO will air a sneak preview of the doc from midnight to 1:30 a.m. Monday, Sept. 19, and then will premiere the film at 8 p.m. Tuesday, Sept. 20. You can watch an exclusive clip of it below: