Pratt, Fletcher <br/><br/>
Secret and urgent, the story of codes and ciphers / 
By Fletcher Pratt.. 
 - Garden city, N.Y. :  Blue ribbon Books,  [1942]. 
 - 282 p. ;  21 cm. 
 - 003.26 (NLA) .
<br/><br/>Includes index. 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Cryptography<br/>Ciphers<br/>Cryptographie
<br/><br/><label>Universal Decimal Class. No.: </label>003.26 (NLA)