Don't ask, don't tell is the common term for the current policy toward gays in the US military. It was introduced in 1993 by President Bill Clinton, although crafted by Colin Powell and has been maintained by his successor, George W. Bush. The policy says that as long as homosexual men and women in the military don't volunteer their sexual orientation, commanders won't try to find them out.
Statistics on the number of persons discharged from the military in the years since the policy was first introduced (1992?) show that more people are discharged now than were before. By this measure, the policy seems to have failed. However, more of these people are given honorable discharges than was the case before. (Hard numbers would be great if anyone has access to them.)