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US NAVY CRYPTANALYSIS

No. 76  MAY 6, 1942 The Navy Department today issued the following communique, based on reports received up to 3 p. m. X Far East X 1 X Several messages from the Navy personnel at Corregidor were received in the Navy Department this morning X Just before the fall of this small island fortress which these men have helped to defend so gallantly, the commander of the naval forces at Corregidor, Capt. Kenneth M. Hoeffel, U. S. N., joined his officers and men in sending a last message of loyalty, devotion, and good cheer to their country, their families and their friends X 2 X Captain Hoeffel reported that the mine sweeper Tanager, and the river gunboat Oahu had been sunk by enemy gunfire from Bataan and that the mine sweeper Pigeon had been sunk by bombers X The river gunboat, Luzon, and the mine sweeper, Quail, were severely damaged by gunfire and were sunk by U. S. forces when capture appeared imminent X All local small craft in the vicinity were demolished by our forces X 3 X When Corregidor fell, there were approximately 175 officers and 2,100 men of the Navy, and 70 officers and 1,500 men of the Marine Corps in the defending forces X Col. Samuel L. Howard is the senior officer of the Marine Corps personnel on the island X It is assumed that all of these officers and men have been captured and will be held as prisoners of war X 4 X So far as is known no casualties resulted from any of the above sinkings X 5 XThere is nothing to report from other areas XX MESSAGE REPEATS XX

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Monkey Point (1998) - The Navy Intercept Tunnel was near here - somewhere!

The USN's Cryptanalysis was distributed amongst units in Washington, Hawaii and the Philippines. Only Washington attacked foreign diplomatic systems and naval codes used in the Atlantic (primarily German). Hawaii had primary responsibility for the Japanese naval systems. The Philippines chipped away at the Japanese fleet cryptographic system, and did some limited diplomatic deciphering, with keys provided by Washington. The unit, which was attached for administrative reasons to the local naval district (the 16th) was installed in a tunnel in Corregidor. The unit comprised 7 officers and 19 men, and had a liason man with its British equivalent in Singapore .It was equipped with 26 radio receivers, apparatus for intercepting both high and low-speed transmissions, a direction finder, and tabulating machinery. Lieutenant Rudolph J. Fabian, then 33, an Annapolis graduate who had three years of radio intelligence experience in Washington, commanded. It was to be the only entire unit which was evacuated from Corregidor.

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The second cable on the top row is of the normal type of international marine cables of the time. Why was it being landed on Corregidor? To be hacked, of course.

This installation is immediately across Enlisted Man's Beach, which faces towards Manila. Beaches are ideal locations for bringing cables on land, because the cables can be landed on a suitable gradient, and because they are unlikely to be disturbed by mooring ships dragging anchors. Inside the blockhouse on the right of the picture are twelve conduits for large cables.  Though severed, it's clear that they were being "landed" from Manila Bay.   The commercial cables, once "landed" secretly, were spliced into, allowing Uncle Sam  to read Japanese Diplomatic and Military Traffic.

 

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The Silent War Against the Japanese Navy
Captain DUANE WHITLOCK  U.S.N. Retired 
Naval War College Review (Autumn 1995)
(reproduced on this site by permission of the Naval War College. All rights reserved.


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 The seaplane ramp. American prisoners were gathered here by the Japanese. Nowadays, it's a tourist beach, beautifully designed by someone who had no sympathy for the place at all.

Even prior to the opening of hostilities, the Corregidor unit had, together with the Singapore unit, commenced the attack and breakdown of JN25. This most widely distributed and extensively used of Japan's cryptosystems, in which about half of her naval messages were transmitted, comprised a code with five digit codenumbers to which were added a key of other numbers to complicate the system. The Navy called it the "five numeral system, " or more formally, JN25b - the JN for "Japanese Navy," the 25 an identifying number, the b for the second (and current) edition. It had made the difficult initial entries, and was in the best position to make new assumptions or confirm or disprove old ones, intercepting messages that the others might not have picked up. Positive or tentative codegroups were flashed from unit to unit via the intercept channel for MAGIC, but the unit's work was interrupted when Fabian, with seventeen other codebreakers, were evacuated by the submarine Seadragon on 4 February 1942, several weeks before MacArthur. The other codebreakers followed later as other submarines made critical evacuations. In all, seventy-five members of the CAST unit were evacuated, the largest single contingent and the only complete outfit to leave the Rock.

Hackers interested in reading more of the history of Cryptoanalysis should read The Code-Breakers by David Khan, Weidenfeld and Nicholson Ltd, 1973 ISBN 0 7221 5146 2

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Until at least 1978, when this was taken, this US Mail post box was near Middleside, hidden in the ipil-ipil undergrowth, alongside the stairway linkimg Middleside to Topside. After the war, when it was decided to reforest the island, ipil-ipil seedlings were dropped from aircraft because unexploded ordinance made it too dangerous to plant trees in the conventional manner.

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The Silent War Against The Japanese Navy

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