This copied from:
http://greenwichmeantime.com/
Each Time Zone is measured relative to Greenwich, England. There are both civilian designations which are typically three letter abbreviations (e.g. EST) for most time zones. In addition there are military designations. These use each letter of the alphabet (except 'J') and are known by their phonetic equivalent. E.G. Greenwich Mean Time (civilian) or Z = Zulu (military and aviation).