Cool! I didn't not know that. I just looked it up out of curiousity: https://www.airandspaceforces.com/article/1091zulu/#:~:text=Since%20Greenwich%20is%20the%20site,call%20sign%20became%20%E2%80%9CZulu.%E2%80%9DAs is typical of the military, it coined its own term. Since Greenwich is the site of the “zero meridian,” they called GMT “Zero Time” or simply “Z- Time.” In the phonetic alphabet that the flyers of the time used to make themselves understood on their radios, “Z” became “Zebra.” When the alphabet was changed, the call sign became “Zulu.”