As Japanese advances in the Philippines threatened CAST, its staff and services were progressively transferred to Corregidor in Manila Bay, and eventually to a newly formed US-Australian station, FRUMEL in Melbourne, Australia.
The US Army Signal Intelligence Service (SIS) break into the highest security Japanese diplomatic cypher (called PURPLE by US analysts) produced very interesting intelligence, but little of military value (except for Ambassador Hiroshi Oshima's despatches from Germany); none of 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.
[citation needed] Furthermore, decrypts from PURPLE traffic, eventually called MAGIC, were rather capriciously distributed to high level officials in Washington, and in general, poorly used.
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.
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.