Orange Grand Maneuvers
The first success that can be directly attributed to the “On-The-Roof Gang” was in response to a large-scale training exercise undertaken by the Imperial Japanese Navy (IJN) in 1930, called the Orange Grand Maneuvers. On 18 May of that year, the “On-The-Roof Gang” operators performing Radio Intelligence (RI) operations at Station BAKER on Guam noticed a sudden and tremendous increase in radio traffic and a higher percentage of encrypted messages contained in the intercept.
Recognizing that something big was happening, the intercept site initiated their first-ever 24-hour coverage on the Japanese exercises, even though they only had nine operators assigned. Over the following weeks, the volume of radio traffic continued to grow, and reached peak on 13 June 1930.
Results of the RI collection of the 1930 Orange Grand Maneuvers, concluded that:
1) The Grand Maneuvers were a dress rehearsal for war, and the maneuvers proved Japan was prepared;
2) The mobilization of the IJN was conducted in secret, and no other intelligence indicators outside of RI recognized this mobilization;
3) The information gained through RI was a direct contributor to the formulation of the U.S. Navy’s own war plans; and
4) The successes of RI gave everyone involved confidence for the future and credibility among U.S. Navy commanders.
This last point cannot be overemphasized. While the “On-The-Roof Gang” and front line leadership understood well the type of advantage RI could provide, the Grand Maneuvers of 1930 demonstrated to Fleet and National leadership that RI was a force multiplier and that the “On-The-Roof Gang” was worth their weight in gold. The “On-The-Roof Gang” was proving itself as an elite and effective intelligence operation.
A concerning issue after the 1930 Grand Maneuvers was related to the proximity of the IJN exercise to Guam. Station BAKER, the Navy’s largest and most capable intercept site at that time, was located on an undefended island which could be captured in case of conflict. Indeed, the 1930 Grand Maneuvers indicated attacking Guam was a part of the Japanese war plan. In order to mitigate this risk, OP-20G immediately drew up plans to increase the RI operations at both Station HYPO in Hawaii and Station CAST in the Philippine Islands, both of which were highly defended and less likely to IJN sneak attack.