23

Planes in daylight

Mic Sandford boasted to military intelligence that his gamble in acquiring Nave had paid off. In February 1943, he wrote to Lieutenant Colonel Robert Little, the assistant director of military intelligence based in Melbourne: ‘Domestic progress has been tremendous. Nave has been quite invaluable. We are now reading air operational traffic of the utmost importance.’1

And thanks to Nave, with so much useful data coming in, Sandford was making plans to send important decrypts directly to the highest levels of command:

Hitherto, however, while a certain amount of it has been used in the field, a good deal reaches us too late to be of any but historic value. Ryan (who is now a Lt. -Col) has arranged to institute two watches on this traffic in the Brisbane area and we are having a teletype line installed. This should enable our air headquarters to receive the information simultaneously with the Japanese.

On the whole, things look much brighter than they did a week ago.2

Eric Nave and Professor T.G. Room, having arrived at Central Bureau after being evicted from FRUMEL in October, were both enjoying success at breaking into army codes. Nave had found the solution to naval air-to-ground codes the previous year, and this had become virtually a production-line process.

But the wireless sections and units to the north were now picking up a different kind of air-to-ground traffic. As the Japanese army increasingly took control of the south-west Pacific operations, the Japanese army air force was more active.

Nave solved this new code with Room’s assistance.3 They had a head start because Nave had a copy of an old Japanese army air-to-ground codebook, discovered by Allied forces in Singapore before the city was captured. The codebook had made its way to Australia (possibly with Norman Webb). It was completely out of date, and none of the current collection of messages was using it, but nonetheless it gave them insights into how the code was structured.

The system used Kana, which was converted into digits and then had additives applied. There were variations from area to area, and the code changed frequently. The call signs were in Kana (or sometimes a combination of Kana and digits), and changed every ten days. Additive books were issued every month.4 With such rapid code changes, reading messages at a timely pace was going to be challenging. Fortunately, it turned out to be a lot easier in practice than the theory suggested.

Nave discovered that, most of the time, the Japanese army air signals officers didn’t bother with additives. If they had a message to send, they would use the codebook to convert it into the standard code, and then just transmit it, completely unenciphered. This was understandable. The officers using this code were mostly pilots and airstrip ground crew. They probably didn’t want to bother with additive encipherment in the middle of a bombing run, or when fighters were providing air cover for a ground battle. Messages needed to be sent quickly.

But because the codebooks themselves didn’t change very often, the message was only hard to crack if the extra work had been put in with the additive encipherment. The result was that Japanese army air-to-ground messages were usually read in full, as soon as they were intercepted, by the local wireless unit or ASIPS team.

For the Allied intercept sites, a message about enemy aircraft movements could reveal the location of those aircraft, almost as clearly as if viewing them overhead in daylight.

Nave’s encyclopaedic knowledge both of code-breaking and of Japanese communication systems gave Sandford another idea. He was planning to establish an intelligence school in Brisbane, capitalising on the concentration of expertise at Central Bureau in Nave and others. Sandford told Little that he hoped to have an ‘extensive training program’ up and running by the end of the year.

A lot of the army air-to-ground messages picked up by the wireless sections turned out to be weather reports. They tended to have a distinct pattern, making them instantly recognisable to experienced Kana operators and ASIPS personnel. Weather reports were of no interest to MacArthur’s intelligence analysts, but Eric Nave had a hunch about how they could be put to use.

These sporadic meteorological reports were almost certainly being sent by Japanese reconnaissance planes. He compiled a collection of them, got hold of data for the timing of recent air raids against Port Moresby and other Allied bases, and matched up each weather report with an air raid. As he suspected, the Japanese reports and the air raids matched up neatly: a few hours before every air raid, a weather report was broadcast. The lag time between the two was the flight time from a Japanese airfield to the target of the raid.

Once Nave made this connection, weather reports on air-to-ground channels took on a whole new meaning. They were effectively air-raid warnings.

Sinkov set Professor Room the task of breaking a code system named JN-16 that Japanese bases were using to send synoptic weather reports to each other. Room managed to turn this seemingly dull and unimportant backwater of the signals landscape into a valuable source of intelligence.

At the time, the only way to get reliable meteorological information was to either use a reconnaissance plane or a weather balloon. The resources of the air force were already stretched, and they could not invest much effort into weather reporting, even though such information was critical for the timing of tactical decisions. With Room’s solution, the air force was able to tap into the Japanese system, accessing the enemy’s own daily weather reports about conditions over enemy territory for free.5 Professor Room acquired a promising young code-breaker, Judy Roe, in early 1943 through AWAS. Judy’s father had told her that she ‘must do something to help the war effort’, then had her assigned to Central Bureau through his friendship with Mic Sandford. Roe, who was later commissioned as a captain, was the first female Australian code-breaker, and the only woman engaged in actual code-breaking — specifically, the study and attempted solution of enemy code and cipher systems. After the war, she became a professor of mathematics at Sydney University.6

The army intercept unit at Coomalie Creek, 51 Wireless Section, tracked the movement of 20 Japanese army bombers eastwards towards Timor over a three-day period. Geoffrey Ballard, who had served in signal intelligence in Greece, Crete, and Palestine, was the intelligence officer on location at the section’s Northern Territory base. On 28 February, he notified the north-west area headquarters of the air force that the bombers had reached Koepang, an airfield on the island of Timor, in preparation for an air raid on Darwin the next day. The air force immediately launched a bombing raid of their own on Koepang.7

Air Commodore F.T. Bredin, responsible for the air raid, commended the wireless section’s work, telling his commander, ‘The successful attack on Koepang aerodrome this morning when twelve aircraft were destroyed on the ground and nine others severely damaged (figured subject to further conformation) was made possible by the information supplied by No. 511 Radio Station over the past few days.’8

Radio signals across the Timor Sea came in clearly from the islands across the water. This was not the case for enemy bases far to the north across New Guinea’s rugged interior, where the towering Owen Stanley mountain range dampened the radio waves, like ripples on a lake hitting a sandbank.

On 29 January, the Japanese army launched an attack on the remote mountain town of Wau, held by Australian diggers — the A Company of the 2/6th Infantry Battalion under Captain W.H. Sherlock. The Australians quickly ran out of ammunition, and Captain Sherlock himself was killed on the first day of fighting as he attempted to charge through enemy lines to safety with only a bayonet for a weapon. Reinforcements and ammunition arrived for the Australians by plane at the Wau airstrip later that day.

A week later, with the battle still raging, eight United States P-39 fighters came in toward Wau to discover Japanese ‘Zero’ fighters and ‘Sally’ bombers strafing and bombing the airstrip and attacking five transport planes coming in to land. The P-39 squadron dived in and engaged with the Japanese attackers, shooting several down while the others departed, but not before the Japanese bombers had destroyed two Dakotas, damaged another, and blown up the Australian signals hut, killing everyone inside. (The ‘signals unit’ at Wau had no intelligence or interception capability; their job was simply to keep A Company in contact with the Australian army command at Port Moresby.)

There had been no warning of the Japanese air attack on Wau; the Owen Stanley mountains stood like silent sentinels, shielding distant Japanese bases from the prying eyes of the intercept units.

If they were too far away from the action, the units could not provide tactical intelligence. The only way to solve this was to raise more units and deploy them further north, closer to the enemy. In late February, a sigint planning group chaired by Mic Sandford recommended the creation of three new wireless units.9