NEW : Gates calls time with troops the `` high point '' of his trip . Defense Secretary Lloyd Austin meets with Iraq troops and commanders . Gates has previously said he will retire Friday . Gates arrived in U.S. on midnight on an unannounced visit .
NEW : Gates calls time with troops the `` high point '' of his trip . Defense Secretary Robert Gates meets with U.S. troops and commanders . Gates has previously said he will retire this year . Gates arrived in Iraq on Wednesday night on an unannounced visit .