In flight testing, THAAD's hit rate is as impressive as it gets.Tested ten times between 2007 and 2013, the U.S. missile defense system has a track record of 100 percent mission success.However, that hasn't stopped some defense experts in the U.S. questioning how reliable it really is.In a report submitted to the U.S. Senate Armed Services Committee last week.the Pentagon's director of Operational Test and Evaluation, Michael Gilmore, said the system has not shown steady progress in its ability to shoot down ballistic missiles in their terminal phase.Pointing to examples where the system had some glitches in poor weather conditions during tests, Gilmore stressed that it was important to fix the problems at hand as THAAD is supposed to be able to work at any time.He also highlighted the need for better training programs for troops who operate and maintain THAAD.The defense official noted that simulators used to train soldiers how to use THAAD are not a completely accurate representation of how the system works in real-life, which could lead to errors when intercepting missiles.THAAD has been a hot topic of debate in Korea as the U.S. has been pushing to deploy the system to South Korea, saying it'll better protect the country against North Korea's ballistic missile threats.Both governments say, however, that the issue has not been formally discussed.But with U.S. Secretary of Defense Ashton Carter's scheduled to visit Seoul early next month, watchers speculate THAAD could be on the official agenda.Kim Hyun-bin, Arirang News.