There is no question traffic analysis played every bit as important a part of intelligence gathering as any other part.
This fact was knowledge officially after the 1933 Japanese Navy Grand Maneuvers.  Quoting from Duane Whitlock’s, On-The-Roof Gang (OTRG) member, Class #20, “The Silent War Against The Japanese Navy.”  In preparing to cover the Grand Maneuver, LT Wenger, USN who had been attached to the staff of Commander in Chief Asiatic Fleet (CINCAF) as Radio Intelligence Officer, arranged to receive all of the intercept material from Station “Shanghai (A), Guam (B) and Philippines (C)  and from two or three temporary intercept sites.  Given the task of deriving intelligence from the material by all methods short of cryptanalysis, LT Wenger spent the next six months performing post-facto traffic analysis.   Out of the effort he produced a 115 page report of the Grand Maneuver in which he laid out in considerable detail the composition and disposition of the forces involved including the identity of the individual ships and commands participating (Naval Order of Battles).

His report was sent back to Washington where it took the small cryptanalytic staff laboring there another three years to recover enough of the new code to affirm that the report produced by LT Wenger was essentially accurate.  From CAPT Holtwick’s History of the Naval Security Group, “The success of ‘traffic analysis’ in giving a picture of the 1933 maneuvers, without the information later from decryption, completely sold the idea of Radio Intelligence to CINCAF Admiral Upham.  The lessons were taken seriously and resulted in a letter from CINCAF which made strong recommendations for the establishment of a major decrypting center in the Ultimate Defense Area and recommended an eventual location on Corregidor Island.”  Corregidor is located in the entrance of Manila Bay, Philippines.

Source: NCVA/ Carl Jensen
Edited By Mario Vulcano