In 1576, Yi passed the military examination (무과; 武科). Yi is said to have impressed the judges with his archery, but failed to pass the test when he broke a leg during the cavalry examination. After he re-entered and passed the examination, Yi was posted to the "Bukbyeong" (Northern Frontier Army) military district in Hamgyeong province. However, he was the oldest junior officer at the age of thirty-two. There, Yi experienced battles defending the border settlements against the Jurchen marauders and quickly became known for his strategic skills and leadership.