As had happened during the Kokoda Track campaign and the Battle of Buna–Gona, estimates by Australian intelligence differed greatly from those at GHQ, as they used different methods. The intelligence staff at Blamey's Allied Land Forces Headquarters (LHQ), headed by Brigadier J. D. Rogers, had come up with a much higher figure of 3,000. I Corps produced an estimate of 1,800, which was passed on along with GHQ's estimate. The Allies' best source of intelligence, Ultra, shone no light on the matter. Finschhafen was mentioned in only five decrypted messages in the previous three months. Most of these were in the insecure Japanese Water Transport Code. Only after the capture of Japanese codebooks in the Battle of Sio in January 1944 were the Allies able to systematically break into the Japanese Army codes. In fact, Japanese strength in the area on 22 September was about 5,000.