Note: It is very difficult to find information on these early stations -
| 1936 | Quarry Heights, Panama | Panama Detachment, 2nd Signal Service Company (Monitoring station No 4 | Established in 1936 by Abraham Sinkov (SIS) |
| 1936 | Fort McKinely, Philippine Islands | 10th Signal Service Det (Monitoring Station No 6) | Station established by Lt Mark Rhodes (SIS) and a small radio detachment. |
| 1938 | Fort Sam Houston, Texas | 7th Signal Service Det (Monitoring Station No 3) | |
| 1938 | Presidio (District of San Francisco), California | 8th Signal Service Det (Monitoring station No 2) | *Not to be confused with the irregular SIGINT station that was operated in the SF area in 1931. That station was a private initiative of Joseph Mauborgne, a colonel destined to rise to the post of commanding general of the Signal Corps before World War II, was assigned to the Presidio. He monitored and recorded Japanese radio traffic as early as 1931 and passed the intercepted coded messages to the Signal Intelligence Service in Washington. These intercepts became part of the earliest grist for the code breakers' mill that solved the Japanese machine cipher known as "Purple" in 1940. These intercepts contributed to the stream of intelligence, code named "Magic," that allowed the Allies unparalleled access to the enemy's plans and greatly contributed to the victory in the Pacific. By 1941, the Presidio had an official, but secret, monitoring station. |
| 1938 | Fort Shafter, Honolulu, Hawaii | 9th Signal Service Det (Monitoring Station No 5) | Established by Solomon Kullback (SIS) in 1936 |
| 15 Oct 1939 | Fort Hunt, Virginia | Monitoring station No. 7 | On September 10, 1939, the National Park Service approved the occupation of the old hospital building at Fort Hunt by A 2nd Signal Service Company Detachment. On 15 October 1939 Lt Robert E. Schukraft and 26 men set up the monitoring station. They shared facilities with the Civilian Conservation Corps (CCC) camp already located there. May have moved to Mitchell Field, NY in 1946. |
| 1930s | Battery Cove, VA | UI Signal Service Unit | |
| 1939 | Fort Hancock, NJ | UI Signal Service Unit | Sometimes referred to as a New York harbor unit |
On 1 January 1939 the five Signal Service Detachments were reassigned to the newly activated 2nd Signal Service Company headquartered at Fort Monmouth. On 1 November 1939 the Headquarters of 2nd Signal Service Company was moved to the Munitions Building in Washington and co-located with the SIS. A small detachment of the Company remained at Fort Monmouth to expand the Cryptographic School.