The infamous phrase sent from Akagi to Nagato announcing a successful attack on the Pacific Fleet in Pearl Harbor. Many different sources claim this phrase means, Tiger Tiger Tiger.

The Japanese word for tiger is actually tora. However Tora seems to have actually been a code word made up of two separate Japanese words. To comes from the word totsugeki, meaning charge or attack. Ra comes from the word raigeki, meaning torpedo attack. So combined they would have a meaning of a charging attack. Any listening posts that would pick up the phrase Tora Tora Tora would more than likely think, Tiger Tiger Tiger and ignore the possible meaning about an attack.

Since there were several American bases attacked on or around December 7th it was essential to keep the attack on Pearl Harbor a secret. Radio transmissions at the time were not easy to scramble there for codes were needed to prevent an enemy from knowing what you were talking about.