HISTORY

during which the aircraft carrier Shōkaku

was severely damaged by three bombs

and required the dry dock repairs. The second aircraft carrier, Zuikaku avoided the

damage however lost a half of her aircraft

crews and waited for the replacements.

Therefore, both ships were missing at the

attack on Midway.

On the other side the American aircraft

carrier USS Yorktown, seriously damaged

in the Corral Sea, was repaired with the

enormous effort and barely withing a

month could join another battle. It was an

unpleasant surprise for Japanese.

Source: US Navy

Ace in the sleeve

Joseph Rochefort

January 2023

USS Yorktown in dock at Pearl Harbor on May 29, 1942. Damage from the Battle of the Coral Sea was repaired

in record time.

passion in solving the rebus and cross

words and recommended him for the Navy

crypto-analytical studies. During 1929-1932

the Navy ensured he could master the Japanese language (including the studies in

Tokyo) a when he was in the beginning of

1941 commissioned to lead HYPO station,

he had already had nine years of service

in the intelligence units under his belt. He

was allowed to personally choose the majority of his team members, so he molded

his team according to his needs. Their main

task was to break the Japanese Navy code

called JN-25 by the Americans.

In cooperation with British, Australian and

Dutch colleagues the American analytics

gradually achieved the capability to read

10 to 15% of each Japanese message. To

estimate the rest of the contents was a

problem. That the large-scale Japanese

offensive was being prepared was clear

even before the first shot were fired in the

Corral Sea. Those in Washington though

supposed that the attack will be directed

to the south, then towards Johnston Island.

And finally estimated the date of the attack

no sooner than middle of June 1942. On

the contrary Rochefort was convinced that

the Japanese operation is headed towards

the central Pacific and its target is Midway

and it will commence in the beginning of

June. And that he was right in all aspects

made him a lot of enemies in Washington.

Luckily, Admiral Nimitz fully agreed with

his conclusions and made the corresponding arrangements. Had he relied on the

Japanese aircraft carrier Akagi at sea in the summer

of 1941. Three A6M Zero fighters are parked forward.

instructions from Washington he would

have reached Midway after its capture by

the Japanese. Instead, he could wait for

Japanese and set the trap for them while

they had no idea about the main American

forces movement.

Trick on Japanese and their own

command

In order to confirm its judgement HYPO

station came up with the deceit Admiral

Nimitz also agreed with. One intercepted

message contained the words “koryaku

butai” which had been confirmed as “invasion fleet” combined with the designation AF. As a target of the attack AF was

mentioned in further Japanese messages.

Rochefort was convinced that AF is Midway. But people in Washington believed

it to be Johnston Island. Then one of Rochefort’s team members, Wilfred “Jasper”

Holmes proposed that Midway faked the

water supply problems. Nimitz gave the

plan green light and the instructions were

sent to Midway by underwater cable. Con-

INFO Eduard

11

Source: Naval History and Heritage Command

The greatest American advantage though

was the intelligence acquired by decoding

the Japanese messages. It helped to uncover the Japanese plan to land at Port

Moresby – and thanks to it the Commader

of the Pacific Fleet, Admiral Chester Nimitz

started to trust the judgment of the HYPO

station on Hawaiian Islands much more

while evaluating the intercepted Japanese

messages. And precisely their information

played the critical role in the case of the

Battle of Midway. It is the proof that even

the nerds can help win the wars!

HYPO station was one of two main cryptographic intelligence unit of the USN in the

Pacific. The other one was in Melbourne.

The third station in Philippines had to be

evacuated before the Japanese onslaught and the personnel was incorporated

into the Australian unit. HYPO station was

commanded by Cpt. Joseph Roschefort, a

very colorful individual in the otherwise

dull uniformed world. Rochefort was born

in 1900 in Dayton, Ohio. In 1917 he enlisted in

the US Navy. During the enlistment process he lied he had been born in 1898 and this

age difference accompanied him throughout his whole career which started by

graduating from the Navy Mechanic School

and starting the service on the tanker USS

Cuyama. There, another officer noticed his