Station CAST Station CAST was the United States Navy signals monitoring and cryptographic intelligence fleet radio unit at Cavite Navy Yard in the Philippines , until Cavite was captured by the Japanese forces in 1942 , during World War II . It was an important part of the Allied intelligence effort , addressing Japanese communications as the War expanded from China into the rest of the Pacific theaters . As Japanese advances in the Philippines threatened , its staff and services were progressively transferred to Corregidor in Manila Bay , and eventually to a newly formed US - Australian station , in Melbourne , Australia . STATION CAST had originally been located at Shanghai but had been evacuated to Cavite in early 1941 as part of the US Navy ' s disengagement with China . Prior to the war , was the US Navy ' s Far East cryptographic operation , under the OP - 20 - G Naval Intelligence section in Washington . It was located at the Navy Yard in Manila and moved into the tunnels on Corregidor , as Japanese attacks increased . STATION CAST possessed one of the PURPLE machines produced by the US Army . Cryptanalytic problems facing the United States in the Pacific prior to World War II were largely Japan ese . An early decision by OP - 20 - G divided responsibility for Japanese cryptanalysis amongst its various stations . Station CAST ( at Manila in the Philippines ) , Station HYPO ( Pearl Harbor , Hawaii ) OP - 20 - 02 , and OP - 20 - G itself in Washington , shared cryptanalytic duties . Other Stations ( on Guam , in Puget Sound on Bainbridge Island , Guam , etc . ) were tasked and staffed for signals interception and traffic analysis . PURPLE diplomatic traffic . The US Army SIS break into the highest security Japanese diplomatic cypher ( called PURPLE by US analysts ) produced very interesting intelligence , but very little of military value , indeed no tactical value , and not much more of direct political value as the Foreign Office in Japan was thought by the ultra - nationalists in effective charge of Japanese foreign and military policy , to be unreliable . Furthermore , decrypts from PURPLE traffic , eventually called MAGIC , were rather capriciously distributed to high level officials in Washington , and in general , poorly used . SIS was able to build several PURPLE machine equivalents and the distribution of those machines has since been thought controversial . One was sent to Station CAST . After the US entered the War , two went to Bletchley Park , the center of British cryptographic work . One was sent to the Far East Combined Bureau ( FECB ) at Singapore , and was lost during the fall of Singapore Japanese Navy crypto systems : JN - 25 . Stations HYPO and CAST were assigned responsibility for work on Japanese Navy systems , and after the agreement with the United Kingdom and Netherlands to share the effort , worked with crypto groups in Hong Kong then Singapore ( Far East Combined Bureau ) and Batavia ( Kamer 14 or Room 14 ) . Prior to the attack on Pearl Harbor , the amount of available traffic was low , and little progress had been made on the most important Japanese Navy system , called by US analysts JN - 25 . JN - 25 was used for high level operations : movement and planning commands , for instance . It was a superencrypted code , eventually a two - book system , and joint cryptanalytic progress was slow . JN - 25B was introduced on 1 December 1940 , but was broken immediately by FECB as the additives were not changed . Most references cite about 10 % of messages partially ( or sometimes completely ) decrypted prior to 1 December 1941 , at which time a new edition of the system went into effect and sent all the cryptanalysts back to the beginning . After 7 December 1941 , there was considerably more JN - 25 traffic as the Japanese Navy operational tempo increased and geographically expanded , and progress against it went better . The FECB contribution stopped until the crypto station could be relocated from Singapore to Ceylon , but CAST , HYPO , and the Dutch at Batavia , in conjunction with OP - 20 - G , made steady progress . CAST during and after the invasion of the Philippines . Station CAST and its personnel and equipment were moved from Manila to the tunnels on Corregidor as the Japanese approached and spent the next months working there . Eventually , they destroyed their equipment ( some IBM punched card machines are said to have been among the gear shoved into the harbor ) and were evacuated by submarine to Australia , for service with FRUMEL . Some personnel also worked at the Central Bureau , supplying signals intelligence to MacArthur ' s South West Pacific Area ( command ) .