If you and your friends wish to share a secret, you can write it in code, and no one else will be able to read it. Codes are one way of writing in secrets. Ciphers(暗码) are another. In the code each word is written as a secret code or word number. In a cipher each letter is changed.
Codes and ciphers have played an important role in the history of the word. Julius Caesar, the Roman ruler who defeated almost all the countries in Europe about 2000years ago, used a cipher when he sent secret messages to his troops. During American Revolution, George Washington’s spies used a kind of code to send him information about the enemy before his military（军事的） action. In World War 2,the American “broke”, or figured out, Japan’s most important navy codes and got enough information to destroy a powerful Japanese fleet（舰队）。
