(Reuters) - The Department of Defense, in a first-of-its-kind move, will allow active duty members of all branches of the U.S. military to don their service uniforms while marching in an upcoming San Diego gay pride parade, event organizers said on Thursday. The move, confirmed in an internal defense memo, marks the first time the military has granted such blanket permission since the September repeal of the "Don't Ask, Don't Tell" policy, under which gay individuals were allowed to serve in the military only if they did not divulge their sexual orientation. "It is our understanding that event organizers plan to have a portion of the parade dedicated to military members," Deputy Assistant Secretary of Defense for Community and Public Outreach Rene Bardorf wrote in an internal memo. "We further understand organizers are encouraging service members to seek their commander's approval to march in uniform and to display their pride," Bardorf wrote. Citing national media attention to the issue, Bardorf granted approval for service members to participate, but limited that approval in scope to the 2012 San Diego Pride Parade only. Nearly 400 military members have already signed up to march in the parade, according to San Diego LGBT Pride, the organizer of the weekend festivities. Many more are expected to participate in the military parade after the announcement went public, Fernando Lopez, the director of public affairs for San Diego LGBT Pride, told Reuters. In a second internal memo published on Thursday, Bardorf said that for parades other than the San Diego event for which he issued a specific memo, local commanders are given discretion in allowing service members to participate unless it is "likely to garner national or international interest or news coverage." The approval for active service members of the Army, Marine Corps, Navy and Air Force to participate in the gay pride parade in uniform comes in the wake of a number of important milestones following the repeal of "Don't Ask, Don't Tell." The U.S. military celebrated gay pride month at the Pentagon for the first time in June, an event that other federal agencies like the CIA had been celebrating for years. More than 50,000 people are expected to attend the San Diego Pride celebration in all, organizers said. Reporting by Mary Slosson; Editing by Alex Dobuzinskis, Cynthia Johnston and Stacey Joyce