Hidden trunk revealed Japanese codes and helped win war in PNG

It was one of the luckiest discoveries of World War II and helped forge Australia’s lasting intelligence* alliance* with the United States.

In the jungles of Papua New Guinea (PNG), an Australian sapper* was sweeping for mines after the retreat* of Japanese troops in January 1944 when his metal detector found an object buried in a stream bed.

It was a steel trunk, hidden and left behind by retreating Japanese troops near Sio, on the Huon Peninsula, because it was too heavy to take with them.

The sapper forced the trunk open to see an astonishing sight – it contained the secret codes for the Japanese 20th Army division, codes the Allies had never properly cracked.

What happened next gave Australian and US cryptanalysts* an edge that accelerated their victory over the Japanese in PNG, according to a new book The Secret History Of The Five Eyes.

Released this week, the book by Australian documentary maker and author Richard Kerbaj shines a spotlight on this largely forgotten incident, which helped build a partnership between Australian and US spy agencies that continues today as part of the Five Eyes* pact.

At the time of the discovery, the US had made solid progress in breaking Japan’s naval codes, helping to deliver crucial victories in the battle of the Coral Sea and at Midway.

In March 1943, Allied code breakers in PNG had also uncovered Tokyo’s plans to reinforce Lae – intelligence that allowed the Allies to ambush* the Japanese fleet in the Battle of the Bismarck Sea, tilting the war in PNG in the Allies’ favour.

The Japanese air force was also thwarted in PNG by an attack on Japanese airfields at Wewak in August 1943 – an operation that came out of the work of Australian-based code breakers.

But the codes of the Japanese army were far harder to crack – until the discovery of the steel trunk.

“In the main, we didn’t have a great deal of success against the tactical (coded army) material,” said US code breaker Major Abraham Sinkov, who was working alongside Australian and other Allied code-breakers at the Central Bureau – the Allied code-breaking centre in Brisbane.

When the steel trunk arrived at the Central Bureau, its contents were so saturated the code breakers were unable to read them.

“Cryptanalysts used any method they could think of to dry out the pages, including hanging some on clothes lines and placing others in front of electric fans,” the book says.

“The books were water-soaked and practically stuck together,” Mr Sinkov said. “We had to separate the pages one by one and … worked out an interesting procedure for swabbing* the page with something like alcohol, I guess it was, which would cause the written material on the page to show up briefly but long enough to give us a chance to take a photograph of it and we were able to reconstruct practically all of this material.”

The ability to read the codes suddenly gave the Australians and Americans clear insight into the shortages of food, ammunition*, ships and other equipment weakening the Japanese forces, which were already in retreat across PNG.

Mr Sinkov and his team of Australians and Americans in Brisbane photographed each page of the material found in the trunk and sent them to Arlington Hall, the US signals intelligence headquarters in Virginia.

With this information, the Allies went from decrypting* 1846 Japanese messages in January 1944 to 36,000 messages in March.

Any hope that Japan had of reversing its losses in PNG were over and the foundations for a lasting intelligence partnership between Australia and the US were fast being laid.

GLOSSARY

• intelligence: secret or confidential information obtained for government and military operations
• alliance: group of countries, political parties or people working together with shared aims
• sapper: soldier who does jobs including laying and clearing landmines
• retreat: tactical withdrawal, pulling back, moving away from an enemy in battle
• cryptanalysts: code-breakers, specialists in the study of codes and ciphers,
• Five Eyes: cooperative intelligence network
• ambush: sudden and surprising attack on the enemy after a period of waiting and hiding
• swabbing: wiping, cleaning, absorbing or clearing moisture away
• ammunition: supply of bullets, shells and bombs that can be shot from a weapon
• decrypting: decoding, converting encrypted data into its original form

EXTRA READING

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QUICK QUIZ

1. Where was trunk buried, who left it there and why?
2. What was the Australian sapper doing when he came across the trunk?
3. Why were the pages of the secret code books a challenge for the Allies and what did they do?
4. What tilted the war in PNG in the Allies’ favour?
5. Allies were decrypting how many messages by March 1944?

LISTEN TO THIS STORY

CLASSROOM ACTIVITIES
1. Classic codes
Some of this army information in the Kids News article was pretty advanced, when you think back to how the world was in 1944.

How do you think military intelligence processes would operate now in 2022, compared to back in 1944?

Divide your page in two, the left side headed THEN (1944) and the right side headed NOW (2022). Write a list of ideas they might still use, and add more advanced modern methods you think the army may use nowadays to gather and hold top secret information.

Time: allow 20 minutes to complete this activity
Curriculum Links: English; History; Digital Technologies; Critical and Creative Thinking

2. Extension
Work with a partner and create a short message. Develop a code to hide that information. You could use letters, dots, shapes etc. Give the message to another partner group to see if they can crack your code. You need to give them a short hint to start.

Time: allow 20 minutes to complete this activity
Curriculum Links: English; Digital Technologies; Personal and Social; Critical and Creative Thinking

VCOP ACTIVITY
A code too hard to crack!
What a discovery! And just in time too.

Have you ever created a secret code so you could communicate to someone “under the radar”?

Think about why you might need a secret code. Who will know the code and who will be kept in the dark? How did you come up with the code?

Write a short narrative answering the above questions and turn it into a short story about using the code to communicate.

Don’t forget to connect with the audience through your VCOP skills.