Carved out of what is now northern Poland by primordial glaciers, the Masurian Lakes are a 20,000-square mile wetland that splits the possible approaches to Eastern Prussia from the east and south. In 1914, they are the land feature that divides the two Russian armies attacking Germany: 1st Army, commanded by General Rennenkampf, that has been resting and rearming for the last five days instead of exploiting their victory at Gumbinnen, and 2nd Army, commanded by Alexander Samsonov, moving up from Russian Poland in the south. The speed of the Russian offensive has caught the Kaiser’s generals off guard, for they did not know that the Tsar kept sixty percent of his peacetime strength in Russian Poland.

The Russian plan is to envelop the defending German army from two sides and destroy it. Unfortunately for the hundreds of thousands of men being led into battle, these two generals have a personal rivalry going back nine years that inhibits their ability to coordinate maneuvers. To make matters worse, the Russian army has sent them into war without any intelligence officers able to read captured German documents — or the available radio encryption technology that would make it possible for them to talk to their national command without being overheard.

Radios will not have great tactical significance in this war, but they already have great strategic value — especially to the Russians, who lack telegraphy and telephony lines in much of Poland. To underline the strategic significance of radio even 100 years ago today, consider that Britain’s first shots of the new war have not taken place in Europe, but in Africa, where the Kaiser’s empire had just finished building the transmitter that links Berlin to her ships in the South Atlantic and Indian Oceans. That campaign ends today when the allies find the station destroyed by the capitulating Germans.

On the Western front, French intelligence will spend the war breaking German encryption and analyzing their communications. But underlining how little tactical use can yet be made of radio technology, no army in this war will field a man-packable radio kit, with important consequences for communications in the trenches. In a very real way, the Second World War will be bloodier, and move faster, simply because radios become ubiquitous among tactical units; but this is not that war.

Not understanding that his rival is not moving to support his attack as planned, and oblivious to the fact that his enemy is operating inside of his decision cycle, General Samsonov marches into a disaster. Called away from his successes in Belgium, General Erich von Ludendorff has used the German railroads to move his outsized army from its defensive positions in the east, leaving only his cavalry to keep Rennenkampf distracted while he achieves superior numbers against Samsonov in the south. When German reservists seem to give way before his attack today, Samsonov pushes his reserves forward without securing his flanks, and after tomorrow he finds himself surrounded.

Out of Samsonov’s command of more than two hundred thousand men, only about ten thousand escape the encirclement after two more desperate days of fighting; the rest desert, are killed, or captured. Shell-shocked and unable to report his failure to the Tsar, on the fourth day Samsonov begs his officers for a moment alone and walks off into the forest to commit suicide.

The Germans are quick to shift their forces to the east again and push Rennenkampf back; it is the last time that Russian soldiers will touch German soil until 1945. Ironically, the encirclement has been made possible by the irascible General Hermann von François, who disobeys orders and delays his attack until expected artillery support has arrived, allowing him to flank Russia’s 2nd Army in the rear. The battle plan has actually been devised by Max Hoffmann, too, but Ludendorff and Paul von Hindenburg accept the victor’s laurels anyway, even though they have spent most of the battle panicking over false reports of Rennenkampf moving to rescue Samsonov.

Ludendorff successfully lobbies Hindenburg to have the Kaiser name the battle for the town of Tannenberg, some thirty miles away, where Teutonic knights were defeated by a Polish-Russian force in 1410. A monument built there will house the remains of Hindenburg, who has been brought out of retirement to preside over this victory. Nazi soldiers dynamite the monument in 1945 before it can fall into Russian hands; Hitler’s sanctuary, Wolf’s Lair, is located nearby.

So it is safe to say that the violent expression of German national identity is forever tied to this ground in East Prussia, which is consequently ripped away to become part of Poland as punishment for yet another great war.

Signals intelligence (SIGINT) has a much longer pedigree than radio, as signals have been passed by semaphore and lantern for centuries, making it possible to read an enemy’s intentions on battlefields all around the world. Yet in our time, there has been a sustained attack on the value of our national SIGINT capability, with many efforts to diminish its value in the eyes of the public at precisely the moment that maintaining any advantage has become harder than ever thanks to the internet and widespread encryption.

A century ago today, 78,000 Russians start dying over four days because General Samsonov has talked ‘in the red’ on a radio — and this is just the opening act of one of the great, and largely untold, war stories of the 20th Century. During the two titanic struggles between these combatants, it is not an exaggeration to say that the signal battle has consequences in millions of lives; if anything, that is an understatement of the case. The signals battle will directly contribute to some of the most famous victories and infamous defeats of the new century, especially here on the Eastern Front: false emitters, broken codes, jamming, and radio direction-finding will all become weapons in a new electronic battlefield.

This story has hardly been told to the public, yet it is the principle reason why Russia and Germany still maintain some of the most advanced SIGINT capabilities in today’s internet-driven world, which in turn requires American intelligence agencies to watch both of them very closely. The notion that we somehow no longer need agencies devoted to spying on the communications of potential adversaries — and even past adversaries made allies — is a blood-soaked lie. We will either have the tools to break secrets or be broken by them.