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In the hustle and bustle of World War II at Pearl Harbor, the door—for a long time—was scarcely noticed. Inconspicuous and unmarked, under an outdoor stairway, it stood at the top of a flight of steps leading to the basement of what was then the administration building of the 14th Naval District. Occasionally, an officer or enlisted man was seen entering or leaving. But it was obvious that whatever lay behind the unmarked door was not open to the public. After the war, the 14th Naval District was abolished, and the former district headquarters became Building #1, accommodating the offices of the Commander Naval Base Pearl Harbor. By that time, the basement was used as storage space—its former arcane functions forgotten.
The Combat Information Unit at Pearl Harbor was subsidiary to the Navy’s Communication Security Section (Op-20-G) in Washington. Another subsidiary station was on the island of Corregidor in Manila Bay. The Security Section and its two branches were code-named Negat, Hypo, and Cast, the contemporary phonetic words for the initial letters of Navy Department, Hawaii, and Corregidor. Their function was analysis of enemy radio traffic through direction finding and cryptanalysis.
A line of radio receiving stations situated on Pacific Ocean islands from the Aleutians southward listened con
tinuously to Japanese transmitters afloat and ashore. a pinpointed them with high-frequency direction fm . „ Ships tried to confuse the listeners by frequently ch'd^cf. call signs, but the receiving stations were rarely }°° £0 they learned to identify vessels by the touch of theirra operator on the key (his “fist”). Thus detecting 1110 j I ments and groupings of Japanese warships, they PaSte their information via Negat, Hypo, and Cast to approp^1 ,(S high-level naval intelligence agencies. Op-20-G an ^ subsidiaries also provided vital information concerning enemy’s plans by intercepting, breaking, and reading coded radio messages. „
Until the raid on Pearl Harbor, Station Hypo in specialized in traffic analysis and decrypting the Japan flag officers’ code. Following the raid, all three stati bent their efforts toward rebreaking System J, the )°v. nese naval operational code. Over the years, the Aa*1 ■ cans had broken the J code many times. The version m by the time of the raid they designated JN (for Japalie^ Navy) 25, the 25th major variation. Just before the ra' j the code had undergone another change, a practice usually heralded a major enemy operation. The Alt' cans, however, overlooked the possibility of an imnW1 attack on Pearl Harbor, partly because their attention focused on a huge southbound convoy en route to inva
l9&
the Navy Department—impressed by Station
Hed h Coclcbreakers of the former Station Cast, who had ljShe ,e <)re ^1C -laPanese advance at Corregidor and estab- >'NNFr,,^emselves m Melbourne, broke an enemy message
alay Peninsula for an attack on Singapore. nianH reac^'n8 Pearl Harbor in late 1941 to assume com- Vj • Pacific Fleet, Admiral Chester W. Nimitz
U| e ^tat'on Hypo. He observed the clattering IBM tab- charors precursors of the computer), asked the officer in few ^C’i ^eUtenant <“ommancier Joseph J. Rochefort, a not • lte questions, and departed. Admiral Nimitz was t° *niPressed. If the Combat Information Unit professed Warn' Ct enemy moves, why had it not given advance v.as,n2 of the Pearl Harbor raid? The answer, of course, Coat fhe Japanese had been careful to keep out of radio rnunication any hint of their plans for the attack. werre^ months passed before Negat and its subsidiaries thgn *}, to recaPture any of the altered JN25 code, and t0 ]■a they could decipher were fragments that added up Scre- Yet Station Hypo, making good use of such M Phs’ was soon accurately predicting enemy moves. ancj , °( its success was due to the example, guidance, Hot n,V'n^ 'ea<Jership of Commander Rochefort, who was in r°r ^avy’s t0P cryptanalyst but was also skilled a 10 procedures and fluent in the Japanese language, the pCar^ ^Pr'* ^42, American and Allied fortunes in acific theater had reached their nadir. In this dark
ajl1 s growing success—called on Rochefort to review po .yai‘able intelligence and come up with the clearest smt: C ^orecast of impending enemy moves. After con-
]a_ nS w>th his colleagues, Rochefort predicted that the tb' nese would soon assault eastern New Guinea and that tVrV0Ulti this operation with a major attack in the ThpC ^Cean' employing their entire fleet.
that pinpointed Port Moresby, the big Australian base in New Guinea, as the probable initial Japanese target. When Station Hypo deciphered a fragment referring to the forthcoming attack as Operation MO, all hands were convinced that Port Moresby was indeed the enemy’s next objective. Observers reported long-range Japanese planes scouting the waters approaching Moresby, suggesting that the assault was imminent, probably in early May.
Thus forewarned, Admiral Nimitz, whose respect for Station Hypo was increasing daily, rushed the Lexington (CV-2) carrier force to the South Pacific to join the York- town (CV-5) force, already there. On 7-8 May 1942, the combined American forces, with additional Australian ships, fought the Battle of the Coral Sea, the first contest between carriers. The Americans sank the light carrier Shoho but lost the big carrier Lexington. Port Moresby, however, was saved. For the first time in World War II a Japanese advance had been blocked. Moreover, the Americans had heavily damaged the carrier Shokaku and stripped the Zuikaku of planes, so that neither would be able to participate in the operation scheduled for the Pacific Ocean.
Much of the intelligence that enabled the Americans to win the decisive Battle of Midway (4-6 June 1942) was derived from codebreaking in Hypo’s basement. The work was expedited by Rochefort’s phenomenal memory, which enabled him to link a newly uncovered fragment with an item that had been deciphered weeks before. When a hot item needed interpretation, Rochefort was likely to consult his longtime friend, Lieutenant Commander Edwin T. Layton, Pacific Fleet intelligence officer. Old friends, Rochefort and Layton had served extended tours of duty in Japan, where they had mastered the difficult language.
Fragments picked up as early as March suggested that the Japanese were planning to invade the Aleutians. By early May, Rochefort and Layton were about convinced that their target in this area was Kiska and one or more adjacent islands, with a diversionary raid on the Aleutian base of Dutch Harbor. During the Battle of the Coral Sea, a decrypted fragment mentioned a new campaign, to be launched apparently before the end of May. Another fragment read: “For current scheduled operations, expedite delivery of fueling hose as follows . . . ,” suggesting that an extended campaign was forthcoming.
The cryptanalysts at Station Hypo were already accustomed to long and irregular hours of deep concentration, in which they lost track of time and forgot such mundane matters as food and sleep. Stimulated by the imminence of a major attack and the imperative need to discover the
53
In subterranean secrecy, a small group of cryptanalysts labored around the clock and broke Japanese codes to give our naval forces two priceless keys to victory at Midway: the Japanese fleet’s time of attack and its direction of approach.
Divisons 1 and 2 would be involved in the assault on
. .” With nothing better to go on, Layton assu: the carriers would approach Midway from due no that is, on bearing 315°. (He later said, “It was jus
gUeSS’”) , The cryph
There remained one last essential: the dates, tnc i
analysts at Station Hypo had recognized time-date gr
inserted in the message fragments, but the time-
groups were re-enciphered, that is, expressed in a ciP ^
inside the code, and nobody at Hypo had been $
break them. From the third week of May on war ,
fthwesn
enemy’s intentions, the basement codebreakers now entered into a period of intense and unremitting brainwork that has become a legend. Laboring night and day, skipping meals, disdaining shaving and bathing, they worked their way through thousands of message fragments in pursuit of crumbs of information—like prospectors panning through tons of muck in hopes of finding a few grains of gold. Rochefort himself padded about in carpet slippers and an old red smoking jacket.
In a fragment decrypted on 11 May, an unidentified naval force was ordered to “proceed direct to Saipan- Guam area and wait for the forthcoming campaign.” Another, deciphered on the 13th, ordered units “concerned with the occupation of MI” to hold a conference on the 26th and depart on the 27th. Another fragment broken that same day mentioned supplies to be shipped for the use of “ground crews on AF.”
Station Hypo had already identified AF as the Japanese geographic locator for Midway. Its association with the letters MI seemed to confirm the identification, but for further proof Admiral Nimitz ordered Midway, via cable, to report by radio in plain language that its distillation plant had broken down. A couple of days later, sure enough, a Japanese message was picked up notifying headquarters that AF was short of fresh water. No doubt remained that Midway was to be the target.
Further decrypted fragments implied that
way. Because Division 5 was not mentioned, Roche and Layton concluded that the Shokaku and the Zut 'f would not participate in the assault. Because the carr‘ were in Japan’s Inland Sea and the occupation force scheduled to depart from the Marianas, they assume the former would support the latter by softening up atoll with air raids in advance of the landings. It s0’ carrier striking force was the key to the whole JaPan ■ attack plan; defeat the carriers, and the attack would c ^ lapse. Hence, it was vital to pinpoint them. A hint ca a message, deciphered 16 May, to the Wake Is weather station, requesting regularly scheduled wea ^ reports. The message included a phrase: “As we ,PlaI-on make attacks from a generally northwesterly direc^
Cryptanalysis
As I Recall. . . Learning
By Captain Joseph J. Rochefort, U. S. Navy (Retired)
While I was serving in the tanker Cuyama in the early 1920s, one of my executive officers was Lieutenant Commander Chester Jersey, and he and I had several things in common. Two of them were bridge and crossword puzzles—they were just coming into style.
When he was ordered to the Navy Department, he remembered my way with crossword puzzles and asked me if I would care to come to Washington on temporary duty in connection with preparing codes and ciphers. It was then that I was introduced to cryptanalysis.
I spent about six months taking a course from Lieutenant Commander Laurance Safford, who really started the Navy’s whole code-breaking organization from about 1923 to 1925. He was the teacher, but there were no formal education processes. He would just turn over several messages and see which member of our group could solve them the quickest. When Safford came due for sea duty, I was ordered to relieve him as officer in charge of the Cryptographic Section in the Office of Naval Communications.
I don’t think it would be an exaggeration to say that when Safford was ordered to the Navy Department to establish this cryptographic section, it was initially for the purpose of improving our crypto systems. In order to do this,
it became apparent to him that a knowledge of worldwide systems m by the British, French, Japanese, or anyone else would be very valuable- So, while still making every effort improve our own systems (which not very good at that time), he also was tackling systems being used by other powers. .
Safford was a true cryptanalyst the sense that he was a technician- who would solve a system just for sake of solving it, but he wouldn t involved in applying the solution t° subsequent operation. Without mea it in an unkind sense, I should exp' that if one desires to be a great cryP analyst, he must be something of an odd character. People like Safford g^ erally do not conform to the accept1-' ideas. As a result, people who have this ability generally require somebo supervising them to keep them on m right track. I’ve often said it is not necessary to be crazy to be a crypt' analyst, but it always helps.
When I first relieved Safford in
arrier
Mid'
iefort
ikaku irriers »was d that p the >, the anese j col- me >n sland rather an to ■ction d that west, ust a
:rypt'
roups
i-date ipher ile to i, ak
concentrated on breaking the time-date groups.
Scribed
what happened next:
hands
th?arently on the verge of success on the 24th, several of dater^Ptana^ysts' Joseph Finnegan and Wesley A. Wright inp fP0lned d'om Dyer and Joe Rochefort) began workmen I|0ll^^ tke n‘ght; for a couple of them, it would be the bro.n -dccpless night in a row. At dawn on the 25th, they dates6-!"6 rc'enc'Pf|ercd code at last and discovered the 6 June~CaiT*er attack on ^ dune, occupation of the atoll on
^alva ^ dasper”) Holmes, Rochefort’s premier traffic die s'd W^° kad been doing what he could to help from Went' e ,nes’ stumbled up the steps from the basement and an «*»* for a little fresh air and sunlight. Along came fiend now assigned to the Yorktown. Holmes later
CaUst h'en [Lieutenant Commander Thomas H.] Dyer me up out of the basement, on his way home at last, k cr the successful conclusion of the time-date cipher fo* Z'.^nder hrs arm was his old lunch box. His uni- ‘00ked as though he had slept in it for three days, ith- was unshaven an(J his hair looked as though wad not been cut for a month. It had not. His eyes [ra'e bloodshot from lack of sleep, and his gait be- dyed how close he was to utter exhaustion. With a aman s contempt for a landlubber, my carrier friend
remarked, “Now there goes a bird who should be sent to sea to get straightened out.”*
On 28 May the Japanese altered their code again, so drastically that the Americans were unable to read it again for many weeks—it no longer mattered. Layton had what he needed. He got to work with his tables and calculating machine. He assumed that the four-carrier force would approach Midway under cover of darkness, launch at first light at extreme range, and then speed toward Midway to shorten the planes’ return flight. Knowing the speeds of ships and aircraft and the time of sunrise at Midway on 4 June, he handed the following estimate to Admiral Nimitz:
“ENEMY CARRIER FORCE WILL APPROACH FROM THE NORTHWEST AND IT SHOULD BE SIGHTED BY SCOUT PLANES AT ABOUT 175 MILES FROM MIDWAY ON BEARING 315 DEGREES, AND THE TIME WILL BE ABOUT 0600 MIDWAY TIME.”
Thus warned, Admiral Nimitz placed his available forces, built around the carriers Enterprise (CV-6), Yorktown, and Hornet (CV-8) on the left flank of the unsuspecting Japanese carrier force as it approached its target.
n "se >r e- to
vere
0
1
n
one the be a <* ininS .lain
'P1'
in
gen-
ted
e
iody
the
.ash'ngton,
the organization consisted
. —VMII, I UO Olg lll/lll IliUl
Wac lV^es Were dealing with at the time s me matt " result ol n- We h,
11 charge what I,
line ti^ at ad 'he messages you have, hem m
vantage in that we got fresh blood in there all the time. Then you get different ideas and approaches to the same problem. Of course, gradually we built up a little nucleus of people who had been in charge of one of the classes and had some special qualification. But this was rather harmful to their careers, because every time one of these fellows went to Washington who had served in this particular division, very few people understood what he had been up to in Hawaii. After all, it was a small organization, known by maybe only a couple of dozen people within the Navy, so recruiting for it was all person-to-person; there was no publicity. As a result, these men became somewhat known as “nuts”—and some of us were.
This excerpt is from a series of recently declassified interviews with Captain Rochefort, conducted in 1969 by Commander Etta-Belle Kitchen, U. S. Navy (Retired) at Redondo Beach, California, for the Oral History Department of the U. S. Naval Institute.
communications and naval intelligence. Communications had the radio sets that could intercept Japanese messages, and they had the radio operators who could be trained to copy Japanese. Linguists who could read Japanese came from the Office of Naval Intelligence (ONI), so that’s how ONI got into the act.
From Safford, I inherited the job of obtaining special typewriters from Underwood. He had started the process, which meant that now radio intercept operators just had to punch keys instead of writing out messages in longhand. He had also started the expansion of the intercept system by opening new stations. He really started the whole thing, and should be considered the father of the Navy’s communications intelligence organization.
At that time, naval officers usually remained on shore duty for only two years. You had to have that system in order to get promoted. That is why Safford remained for only two or two- and-a-half years. I remained two years, and so forth. This was possibly an ad
tig me uicdodgcb you nd
lhem em UP *n various ways, write them °pe ktdow 'he other, and stare at nite p., rehy soon, you’d notice a defi- try va.lern among the messages. You y0„.r ‘0US solutions, and eventually, if 'hakes U^y and 'he other fellow
™**es—which he invariably
h°n th "en you come UP w'th a solu- q at will stand up under test.
thing rJodebreaking effort was some- 0 3 joint operation between nava
j tk ^ wtdimg wnii ai me uii
as a r6 lnatter °f recovery assistance ineSa'k °f 'he 1923 earthquake in j ' ^ had classes when I was of with charge, and I’d have people sti You | ,at ^ caH “the staring process.
Of m- uiganizauun consisie
CePtioSeii aS °^‘cer in charge, an ex- ^gnesn • caPable cryptanalyst named assjStarisco11’ one helper, and one ties- ik1' W*10 kad no particular abili- Ple 'weat Was b- With these three peo- Haval S<?Ved tke i>rst major Japanese Servesnei system’ and ASgie de- '"essanL tke cred*t- The big item their
W;
|9«-1
r°ceed|
,nKS / August 1983
55
* W. J. Holmes, Double-Edged Secrets: U. S. Naval Intelligence Operations in the Pacific During World War II (Annapolis: Naval Institute Press, 1979), p. 95.
LtEC/TENANjT COMMANDER JOSEPH * "DININ'OR"• VC .-ANALYZEV JAPANESE'WAL RADIO TRAFFIC- AND PL TV ED /■ VAT OR ROLE IN BRE.V-V.NV THE. ENEMY'S ^PtNCTTAL NAVAL CODES. THEY THUS EXPOSED ENEMY FEANS AND OPERATIONS,. “MERSEY ENAS LINS U 3 ffAYAE.FORCES 73 ATTAIN VICTORIES. IN SUCH. "•'EY BATTLES; AS CORAL SEA AND MIDWAY, TURNING'POINTS •!'•' THE TAR IN'THl
l4fR NAVAL OiSTRICT.. UNDER THE INSPIRE? LEADERSHIP-OF l
CH. 1941-42^ IN THE EASEMENT T THE FOOT 0 F THESE STAIRS, DEDICATED OFFICERS AND HEN OF THE COME.' T r-EEUG'fitfcS' UNIT,
v
§T
• v-. *
■NT"
ruiiuwuig me Ddinc ui ivuuwaj, moved Station Hypo from its basement to a building ^ ^
a new name: Fleet Radio Unit Pacific (FruPaC^
coi made an
only react to Allied offensives. The codebreakers m -
immense contribution, however, in keeping Am.e ^>a, submarines informed of the routes, destinations, an ^ ^ *
positions of enemy convoys, which Japanese shipper
j-^y rorltn And * ^
Admiral Yamamoto’s timetable as he set out on anj>lSPe.
tion tour of Japanese bases in the South Pacific-
1 Uiv ~ i
aadalc^
fighter planes that shot him down precisely on sche
COMBAT INTELLIGENCE UNIT
I4TH Naval district
WORLD WAR II
For years, the basement where the outcome of World War II in the Pacific may very well have been determined went unnoticed. The doorway which led to it resembled thousands of other doorways at hundreds of military bases. But after four decades, the basement was rediscovered and honored with a plaque.
Just before 0600 on the morning of 4 June, Lieutenant Howard Ady, flying in his Midway-based PBY Catalina, was the first to sight the Japanese carrier fleet—coming out from under the edge of an overcast. He stared in awe. It was, he said, like “watching the curtain rise on the Biggest Show on Earth.” As soon as he had seen two of the carriers emerge, he flashed his report: “Two carriers and battleships bearing 320°, distant 180. course 135°, speed 25.” Off to the northeast, the U. S. carriers launched their attack. At Pearl Harbor, Admiral Nimitz remarked to Commander Layton, “Well, you were only
five miles, five degrees, and five minutes off. ^ .oUS Most Americans know what happened on this g 0 Fourth of June.” Getting the jump on the Japanese virtue of Hypo’s forewarning, the Americans sank thre ^ the Japanese carriers that morning and destroye fourth before the end of the day. As a result, the wa*_ turned completely around. The Allies, after six mon ^ the defensive, now seized the offensive, which they nt-
relinquished. Mimitz
Following the Battle of Midway, Admiral
cent to his new headquarters at Makalapa, just acr°uvpo road from the Pearl Harbor shipyard. Here, Station ) ,
The cryptanalysts exposed no more major attack P'an* ^ the enemy, for the Japanese, now on the defensive c
thorities unwarily controlled by radio. And ^
achieved one more big coup by breaking and „
V
Americans, relying on FruPac’s information and the ad^ ral’s known passion for punctuality, sent Gu
, pwv.av., ^ jS.
Station Hypo’s basement was inherited by the w & tered Publication Issuing Office (RPIO), Pearl, whic ^ ,f tributed codes and ciphers to U. S. ships and station-^ ^ the Pacific Ocean areas. Now over the door aPP^Le. sign: Communication Security Material Issuing O ^ Communication officers and their enlisted assistants scended the stairs and stood before one of a line of aP j tures resembling bank windows. Here, they P^T^s their credentials and were issued the appropriate edt > of codes and ciphers, which they carried away in se mailbags. w
After the war, RPIO, Pearl, moved into more m° ^ quarters, and the basement fell into disuse and then came a storage area. In the mid-1960s, historians, sec
momentous achievements of the officers and men labored there. 0f]
When their findings were brought to the attend0 ) j
T A Hifnmnna r>n*-v-\t-n<1 n/J 1 n(1 Apfi/'or nf tVlC * < I
refurbished. In a March 1983 ceremony, a plaque ^,| affixed to the outside wall, commemorating the vital ^
sor Emeritus of History at the U. S. Naval Academy. During. Y'gjjifj I II, he served as executive officer of the Registered Publication ^ I
Office (RPIO) at Pearl Harbor. Through his urging, the basement , j
sir
information about the Battle of Midway and the u«*- ^ of radio intelligence on the outcome of World War
rediscovered the basement and revealed the story
Captain T. A. Mamane, commanding officer of the • - ^ i Harbor Naval Shipyard, he had the basement cleared ^
of the codebreakers who fought World War II in the ce
Dr. Potter, author of Nimitz and other books on naval history,15 * • ,uiVr j
, World " i
the 14th Naval District Combat Intelligence Unit deciphered so 1 important Japanese codes was finally dedicated as a memorial to group’s monumental contribution to victory.