Spy Tech: The GPS Numbers Station

June 8, 2026 by Al Williams 21 Comments

We’ve talked before about number stations — mysterious shortwave transmitters repeating numbers, presumably for clandestine purposes. But, of course, the mere fact that they are unusual makes them stand out. The best place to hide something is in plain sight. In the old days, a broadcaster might slip a fake news story in mentioning a name that has a secret meaning, for example. But according to [Steven Murdoch], the United States has an even more obvious hiding place for a numbers station: inside GPS.

Every L1 C/A navigation message is a 176-bit field known by the affectionate moniker: Subframe 4, Page 17. The GPS specification says it is for “special messages.” No one has disclosed what those messages might be.

[Murdoch] at University College London analyzed over 12 million GPS packets from 2007 to 2026, trying to understand what was in this field. You might think 176 bits isn’t much, and you are right. But the L1 C/A signal carries 50 bits per second, and each frame is 1,500 bits. As [Murdoch] points out: “every bit must earn its place.” Each subframe is 300 bits, so this mysterious signal is 12% of the subframe. It must be important to someone.

Continue reading “Spy Tech: The GPS Numbers Station” →

Spy Tech: A Quiet Radio For Spies

May 20, 2026 by Al Williams 9 Comments

Normally, when you think of a radio transmitter, you want the strongest signal and range. But if your radio operator is secretly operating as a spy, broadcasting their position isn’t a feature; it is a liability. This fact didn’t escape World War II radio designers.

In late 1942, the British realized they needed a way for Special Operation Executive agents, resistance members, and other friendly forces to communicate with an aircraft without attracting undue attention. Two engineers from the Royal Corps of Signals developed a pair of transceivers — the S-Phone — operating around 380 MHz just for this purpose. Frequencies this high were unusual at the time, which further deterred enemy detection.

The output power was below 200 mW, and the ground equipment consisted of a dipole strapped to the operator. No transistors, so with rechargable batteries, the rig weighed about fifteen pounds and reused some parts of a paratrooper radio, Wireless Set Number 37. The other side of the connection was installed in an airplane.

Continue reading “Spy Tech: A Quiet Radio For Spies” →

Spy Tech: Conflicts Bring A New Number Station

March 30, 2026 by Al Williams 23 Comments

If you know much about radios and espionage, you’ve probably encountered number stations. These are mysterious stations that read out groups of numbers or otherwise encoded messages to… well… someone. Most of the time, we don’t know who is receiving the messages. You’d be excused for thinking that this is an old technology. After all, satellite phones, the Internet, and a plethora of options now exist to allow the home base to send spies secret instructions. However, the current-day global conflict has seen at least one new number station appear, apparently associated with the United States and, presumably, targeting some recipients in Iran, according to priyom.org.

As you might expect, these stations don’t identify themselves, but the Enigma Control List names this one as V32. It broadcasts two two-hour blocks a day at 0200 UTC and a repeat at 1800 UTC. Each message starts with the Farsi word for “attention” followed by what is assumed to be some header information as two 5-digit groups. Then there is a set of 181 five-digit groups. Each message is padded out to take 20 minutes, and there are six messages in each transmission.

Continue reading “Spy Tech: Conflicts Bring A New Number Station” →

SpyTech: The Underwater Wire Tap

March 5, 2026 by Al Williams 20 Comments

In the 1970s, the USSR had an undersea cable connecting a major naval base at Petropavlovsk to the Pacific Fleet headquarters at Vladivostok. The cable traversed the Sea of Okhotsk, which, at the time, the USSR claimed. It was off limits to foreign vessels, heavily patrolled, and laced with detection devices. How much more secure could it be? Against the US Navy, apparently not very secure at all. For about a decade starting in 1972, the Navy delivered tapes of all the traffic on the cable to the NSA.

Top Secret

You need a few things to make this a success. First, you need a stealthy submarine. The Navy had the USS Halibut, which has a strange history. You also need some sort of undetectable listening device that can operate on the ocean floor. You also need a crew that is sworn to secrecy.

That last part was hard to manage. It takes a lot of people to mount a secret operation to the other side of the globe, so they came up with a cover story: officially, the Halibut was in Okhotsk to recover parts of a Soviet weapon for analysis. Only a few people knew the real mission. The whole operation was known as Operation Ivy Bells.

The Halibut

The Halibut is possibly the strangest submarine ever. It started life destined to be a diesel sub. However, before it launched in 1959, it had been converted to nuclear power. In fact, the sub was the first designed to launch guided missiles and was the first sub to successfully launch a guided missile, although it had to surface to launch.

Oddly enough, the sub carried nuclear cruise missiles and its specific target, should the world go to a nuclear war, was the Soviet naval base at Petropavolvsk.

Continue reading “SpyTech: The Underwater Wire Tap” →

Spy Tech: The NRO And Apollo 11

September 25, 2025 by Al Williams 13 Comments

When you think of “secret” agencies, you probably think of the CIA, the NSA, the KGB, or MI-5. But the real secret agencies are the ones you hardly ever hear of. One of those is the National Reconnaissance Office (NRO). Formed in 1960, the agency was totally secret until the early 1970s.

If you have heard of the NRO, you probably know they manage spy satellites and other resources that get shared among intelligence agencies. But did you know they played a major, but secret, part in the Apollo 11 recovery? Don’t forget, it was 1969, and the general public didn’t know anything about the shadowy agency.

Secret Hawaii

Captain Hank Brandli was an Air Force meteorologist assigned to the NRO in Hawaii. His job was to support the Air Force’s “Star Catchers.” That was the Air Force group tasked with catching film buckets dropped from the super-secret Corona spy satellites. The satellites had to drop film only when there was good weather.

In the 1960s, civilian weather forecasting was not as good as it is now. But Brandli had access to data from the NRO’s Defense Meteorological Satellite Program (DMSP), then known simply as “417”. The high-tech data let him estimate the weather accurately over the drop zones for five days, much better than any contemporary civilian meteorologist could do.

When Apollo 11 headed home, Captain Brandli ran the numbers and found there would be a major tropical storm over the drop zone, located at 10.6° north by 172.5° west, about halfway between Howland Island and Johnston Atoll, on July 24th. The storm was likely to be a “screaming eagle” storm rising to 50,000 feet over the ocean.

In the movies, of course, spaceships are tough and can land in bad weather. In real life, the high winds could rip the parachutes from the capsule, and the impact would probably have killed the crew.

Continue reading “Spy Tech: The NRO And Apollo 11” →

Spy Tech: Making Microdots

August 17, 2024 by Al Williams 18 Comments

It isn’t just a spy movie trope: secret messages often show up as microdots. [The Thought Emporium] explores the history of microdots and even made a few, which turned out to be — to quote the video you can see below — “both easier than you might think, and yet also harder in other ways.”

If you want to hide a secret message, you really have two problems. The first is actually encoding the message so only the recipient can read it. However, in many cases, you also want the existence of the message to be secret. After all, if an enemy spy sees you with a folder of encrypted documents, your cover is blown even if they don’t know what the documents say.

Today, steganography techniques let you hide messages in innocent-looking images or data files. However, for many years, microdots were the gold standard for hiding secret messages and clandestine photographs. The microdots are typically no bigger than a millimeter to make them easy to hide in plain sight.

Continue reading “Spy Tech: Making Microdots” →

Spy Tech: Unshredding Documents

June 12, 2023 by Al Williams 38 Comments

Bureaucracies generate paper, usually lots of paper. Anything you consider private — especially anything that could get you in trouble — should go in a “burn box” which is usually a locked trash can that is periodically emptied into an incinerator. However, what about a paper shredder? Who hasn’t seen a movie or TV show where the office furiously shreds papers as the FBI, SEC, or some other three-letter-agency is trying to crash the door down?

That might have been the scene in the late 1980s when Germany reunified. The East German Ministry of State Security — known as the Stasi — had records of unlawful activity and, probably, information about people of interest. The staff made a best effort to destroy these records, but they did not quite complete their task.

The collapsing East German government ordered documents destroyed, and many were pulped or burned. However, many of the documents were shredded by hand, stuffed into bags, and were awaiting final destruction. There were also some documents destroyed by the interim government in 1990. Today there are about 16,000 of these bags remaining, each with 2,500 to 3,000 pieces of pages in them.

Machine-shredded documents were too small to recover, but the hand-shredded documents should be possible to reconstruct. After all, they do it all the time in spy movies, right? With modern computers and vision systems, it should be a snap.

You’d think so, anyway.

Continue reading “Spy Tech: Unshredding Documents” →