TheCodeBreakers
The Tokumu Han cryptanalysts succeeded best with BAMS, the two-
part superenciphered Allied merchant ship code. They solved about half
of the BAMS intercepts. How Were they suddenly able to do so well with
so relatively difficult a system? Germany had given them the basic BAMS
codebook, which had been captured by her raider Atlantis. Consequently,
the Japanese had only to remove the superencipherment. BAMS provided
occasional tidbits pf information—three transports had departed from
Cal-tfornia, for example, or a vessel's course and speed data— out even
here, Ozawa complained, "By the time the code
[message] was broken, the ship was no longer in the original area."
The Tokumu Han expended most of its cryptanalytical energies on the
CSP 642, the strip cipher, which the U.S. Navy regarded as its lowest-
echelon system. The Navy complicated it by not using the full
complement of 30 strips every time. Instead it eliminated from zero to five
strips from one day to another
annaabi.ee 
