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Part two of Matt Zullo’s study of activities of the US Navy’s radio interception service in the Pacific looks at their service during the Pacific War. Part one looked at the establishment of this service – starting with a few individuals in the 1920s, and really starting to expand when a training school for katakana interception was set up on the roof of the main US Navy building in Washington, D.C. (thus the nickname of the On-the-Roof Gang’). Here radio operators were taught how to listen to and record the Japanese Navy’s version of Morse Code, which was used to transmit the 48 characters of the katakana script.
This book starts in the aftermath of the Japanese attack on Pearl Harbor, an attack that went undetected by the intelligence services, an intelligence failure that the author describes as ‘perhaps the worst in modern history’. It had been clear for some time that war with Japan was likely, but a combination of excellent Japanese operational secrecy and US assumptions that the initial attacks would be in the Philippines meant that the Japanese attack on Pearl Harbor came as a surprise on the day.
When the Japanese attacked, the US intercept service had bases on Guam, the Philippines and Hawaii, which between them had 75% of the active duty members of the ‘On-the-Roof’ gang. Of these the base on Hawaii was only in direct danger on the day of the attack itself. Guam was very quickly overrun and the eight man team on the island captured, although not identified as intelligence specialists. The much larger team in the Philippines, by then based on Corregidor, were soon in danger of the same fate. We follow the very different fates of the Guam and Philippines teams. The Guam team ended up in a POW camp in the Japanese home islands, where their most reliable way of telling how the war was going was how badly they were treated by their guards. The Philippines team was evacuated by submarine and ended up in Australia, where they were soon operating again.
The intercept teams were able to provide two different levels of intelligence. They are best known for providing the raw material used by the Navy’s cryptographers to produce the ‘Magic’ intelligence (the US version of Ultra), a top secret programme to break Japanese codes whose results were only passed onto the most important American leaders, starting with the President, General Marshall and Admiral King. This is the level of intelligence that led to the discovery of the Japanese plan to attack Midway. However they were also able to provide much lower level intelligence – a lot of low level tactical messages weren’t encrypted because it simply wasn’t practical (from aircraft for example), so these messages could be used more immediately.
Teams of operatives were posted onboard warships, and could give the information they intercepted directly to the officers onboard. Another example were the daily messages broadcast from the naval base at Truk to the picket ships guarding the approaches to that base, to inform them of the following day’s ship movements. A system was soon set up to pass this information directly to the commanders of the US submarines patrolling outside Truk, allowing them to attempt to intercept these ships (at least three Japanese carriers were damaged as a result of this intelligence).
One of the most affecting elements of the story is the experiences of the men captured on Guam, during their time in captivity in Japan. Their time in captivity wasn’t quite as brutal as some, but it was still a terrible time.
As with the first volume, the story is largely told from the point of view of the individuals involved. The author worked in this discipline for forty years and has been studying this topic for more than twenty. He meet or corresponded with four of the On-the-Roof Gang, and had access to the archives of the National Cryptologic Veterans Association, which contained much information about the Gang. This style works well for this story, really bringing us into the world of the ‘Gang’. This is a fascinating story, well told by an author who very much understands the topic.
Chapters
1 – Chaos at Heeia
2 – Guam Attacked
3 – The Philippines Under Attack
4 – Attacks across the Pacific
5 – Hiding in the Jungles of Guam
6 – Operations at Station CAST
7 – Captured
8 – Blackout at Station S
9 – Plans for Station CAST
10 – Oahu Begins to Recover
11 – Life in Dulce Nombre de Maria Cathedral
12 – Gamatron Island
13 – The Fight in the Philippines Continues
14 – Leaving the Church
15 – Radiomen Arrive at Pearl Harbor
16 – Argentina Maru
17 – Class #25X
18 – Recoveries at Station CAST
19 – Arrival at Zentsuji
20 – Station HYPO Moves to Wahiawa
21 – Safford’s Fate
22 – The Vanishing
23 – POWs Put to Work
24 – The First Radio Intelligence Unit
25 – The In-the-Attic Gang
26 – Crisis on The Rock
27 – USS Permit
28 – Messages to Home
29 – Life on Corregidor
30 – The Doolittle Raid
31 – Arrival in Melbourne
32 – Zentsuji after the Doolittle Raid
33 – The RZP Campaign
34 – The Last Corregidor Evacuees
35 – The Battle of the Coral Sea
36 – Heroics in Hawaii
37 – The Battle of Midway
38 – Zentsuji after Midway
39- Wildman Volunteers
40 – FRUMEL Operations
41 – HYPO on a Roll
42 – Arrival in China
43 – Redmans in Charge
44 – Arrival in Guadalcanal
45 – Happy Valley
46 – Red Cross Delivery
47 – The Battle of Guadalcanal
48 – NI HO HI
49 – The Battle of Tassafaronga
50 – Tomorrow Messages
51 – The Black Market
52 – USS Whale
53 – Japanese Evacuation of Guadalcanal
54 – Station AA
55 – Nebraska Avenue
56 – The Battle of the Bismarck Sea
57 – March Optimism Fades
58 – Adak
59 – Yamamoto’s Itinerary
60 – Yamamoto’s Flight
61 – Competitions at Zentsuji
62 – The Battle of Attu
63 – Bainbridge Training
64 – Kunming
65 – Plans for Kiska
66 – The Battle of Kiska
67 – Kuril Islands
68 – Death at Zentsuji
69 – A New Mission in China
70 – Tarawa
71 – Journey to the Gobi Desert
72 – Plans for Truk
73 – Operation Hailstone
74 – The Battle of the Philippine Sea
75 – Retaking Guam
76 – Orders to Melbourne
77 – A Battle Royale Shapes Up
78 – The Battle of Leyte Gulf
79 – Rice Scrapings
80 – The Destruction of Tunnel AFIRM
81 – Bombing Osaka
82 – Zentsuji after the Bombing of Osaka
83 – The Battle of Iwo Jima
84 – Okinawa
85 – IJN Yamato
86 – USS New Mexico
87 – Markle’s Fire
88 – The Crew of USS New Mexico
89 – Target: Japan
90 – Plan for Operation Downfall
91 – Leaving the Gobi
92 – Flyover
93 – Surrender
94 – Prisoners in Control
95 – Hawaii Celebrates
96 – Release and Relief
Epilogue
Author: Matt Zullo
Edition: Paperback
Pages: 438
Publisher: ZooHaus
Year: 2026