长 here is read zhǎng (3rd tone, 'chief / head'), not cháng (2nd tone, 'long'). Same character, two readings: zhǎng = 'leader' (
校长 'principal,'
厂长 'factory director,'
总参谋长 'chief of staff'); cháng = 'long' (
长城 'Great Wall,'
长跑 'long-distance running'). Misreading the tone here would change 'Chief of Staff' into nonsense ('long staff officer').
