The Oryn Link was a masterpiece of isolation, but in the muddy darkness of the estuary floor, it was blind. Deacon knew the Imperial Navy's "Diving Corps"—a specialized unit of penal laborers and alchemists—had already been seen testing heavy, brass-domed helmets in the harbor of Solstice. If they found the cable, they wouldn't cut it; they would clamp an induction-thimble onto the iron armor and bleed the North's secrets into the deep.
"We can't patrol two miles of seabed with rowboats," Miller said, looking over the blueprints of the armored cable. "By the time we see bubbles on the surface, the tap is already installed. We need to hear them coming."
Deacon turned to the phenomenon he had discovered during the "Magnetic Pulse" incident. He began developing the Oakhaven Hydro-Acoustic Sensor. It was a primitive precursor to sonar, utilizing a sensitive carbon-pile microphone housed in a pressurized copper bell, anchored every five hundred yards along the cable route.
"The water is an incredible conductor of vibration," Deacon explained to the newly formed 'Cable-Guard.' "The clink of a wrench against the iron armor, the rhythmic hiss of a diver's air-hose, or even the churning of an Imperial screw-propeller—the sensors will pick it up. We'll hear the estuary breathing."
The "gritty realism" of the underwater war was a battle of silence. Deacon established the Listening Post in a damp, reinforced cellar at the Rail-Head. Operators sat with brass stethoscopes pressed to their ears, listening to the strange, haunting symphony of the deep: the grinding of silt, the clicking of crustaceans, and the distant, low-frequency groan of the tides.
The first contact came on a Tuesday night during a heavy fog. The lead listener, a blind former miner named Elias who had an uncanny sensitivity to vibration, suddenly raised a hand.
"Iron on iron," Elias whispered. "Mile marker 1.2. It's slow... rhythmic. Someone is scraping the barnacles off the armor."
Deacon didn't send the militia. He engaged the Acoustic Disrupter. He had Miller gear a small, high-pressure steam piston to a heavy iron plate submerged near the Rail-Head pier. By releasing a series of rapid, high-intensity pulses into the water, he created a wall of sound that was harmless on the surface but agonizing to anyone submerged in a brass helmet.
The effect on the Imperial divers was devastating. Underwater, the sound didn't just hit the ears; it vibrated the bones and rattled the teeth. Three hundred yards away, the Imperial diving-bell was forced to surface. The divers emerged disoriented and nauseated, their ears bleeding from the pressure-waves. They hadn't seen a single Oakhaven soldier, but they had been repelled by the water itself.
"The Steward is going to call this 'Underwater Sorcery,'" Julian warned, watching the Imperial barge retreat into the fog. "He'll use it as an excuse to bring the Navy's 'Ironclad' into the estuary to 'secure the shipping lanes.'"
"Let him bring the Ironclad," Deacon said, his eyes fixed on the vibration-logs. "He's fighting a 19th-century war with 18th-century ears. We've turned the estuary into a giant sensor array. Every move he makes is a signal we can read."
But the "Silent War" had an internal cost. The constant acoustic pulses were disrupting the local ecology. Dead fish began to wash up on the banks of Oryn-West, and the local "Drifter" fishermen, already hostile, were now bordering on open revolt. They saw the "Iron Lord" as a monster who was murdering the sea to protect a wire.
Deacon had to innovate again, this time to save his reputation. He adjusted the frequency of the sensors to a range above human (and fish) hearing, utilizing the Galton Principle. By moving the acoustic defense into the ultrasonic spectrum, he maintained the security of the cable while silencing the complaints of the shore.
The estuary became a graveyard for Imperial ambition. Five more attempts to tap the cable were thwarted by the "Silent Screamer," as the divers began to call it. The Oryn Link remained the only secure line of communication in the Empire, a copper nerve buried in a fortress of sound.
"We've secured the water, David," Miller said, looking at the clean telegraph logs. "But the Steward is building something new in the South. The spies say he's no longer looking at the water or the air. He's looking at the Vacuum."
Deacon felt a chill. If the Empire was experimenting with vacuum-tube physics, they were moving toward the one thing that could bypass his acoustic and magnetic defenses: Wireless Radiation.
"Then we move to the next stage," Deacon said. "If he wants to talk through the void, we'll give him a void he can't speak through. We're going to build the Oakhaven Faraday Cage—not for a room, but for the entire valley."