The five-eighths-inch iron bolt sheared off under the massive torque of Danial's socket wrench with a sharp, metallic SNAP that echoed through the lower staging yard of Sub-Level 7 like a pistol shot.
Danial did not stop to clear the broken bolt. He immediately grabbed his hardened iron punch and heavy mallet, driving the ruined shank out of the steel angle bracket with three rapid, precise strikes before alignment-lining the next reinforcement plate.
Around him, Node 6's lower staging floor had been converted into a full-scale, bustling military workshop. Thirty miners from Sector 4 had descended the southern incline over the past three hours, carrying heavy structural I-beams, timber shoring posts, spare boiler plates, and three hundred feet of high-pressure reinforced rubber hose salvaged from the lower maintenance yards. The ambient heat in the cavern had settled into a dense, tropical warmth, but nobody slacked their pace.
"Bring that twelve-inch I-beam up!" Gears bellowed from the catwalk high above, guiding a two-ton structural steel beam suspended from an overhead chain hoist. "Set the lower shoe directly into the basalt floor slot! We're anchoring this bulkhead against five-inch high-explosive mortar shells, not just small-arms fire!"
The miners worked in tight, disciplined pairs, their bare shoulders glistening with sweat and graphite grease. There were no long speeches, no orders wasted, no hesitation. These were men who had spent their entire working lives timbering dangerous cave-ins and bracing three-thousand-pound rock falls in the deep salt seams; building an iron barricade was simply heavy timbering with steel plates and cold rivets instead of pine logs.
Maya stood near the western wall of the chamber, her leather drafting board set up on an upside-down wooden oil drum. She was rapid-drafting structural load diagrams using white chalk on black slate, calculating the exact angle of kinetic deflection needed to keep the rock ceiling from shattering under concentrated artillery fire from above.
"Danial," Maya called out, pointing her chalk stick at the upper arch of the cavern ceiling where the dark basalt met a vein of pale grey slate. "Look at the stress lines in the stone above Node 6. The main granite shelf is solid, but the slate seam running sixty feet directly above the boiler shell has three major shear fractures from the '41 collapse."
Danial walked over, wiping a mix of sweat and graphite grease off his forehead with the back of his bare arm. He looked up to where her chalk pointer was aimed, his eyes narrowing as he evaluated the structural geometry of the ceiling.
"If Sterling's sappers land a mortar shell directly on that upper slate seam," Danial analyzed, his thumb tracing an imaginary line of force through the air, "the shock wave will travel down the fracture line and shear off the primary ceiling pins holding Node 6's overhead crane rail."
"Which drops ten tons of iron crane directly onto the main steam header," Maya concluded, her chalk snapping cleanly between her fingers under the intensity of her pressure calculations. "If that header ruptures from above, the thermal back-pressure will vent inside this room instead of going to the city. We need to brace the slate seam from below before their first battery opens fire."
"We can't brace sixty feet of open air with standard steel beams, Maya," Danial said, looking up at the high, shadowy vault. "We don't have the materials, the structural timber, or the crane capacity to erect a seventy-foot vertical tower in time."
He paused, his eyes shifting abruptly to the two three-inch secondary steam lines running off Node 6's primary boiler shell. A sharp, practical engineering realization lit up his face. He walked over to the secondary line, tapping his knuckles hard against the schedule-forty steel pipe until it rang clear.
"If we weld four closed-end iron extension rams between the ceiling slate and the boiler foundation plates, and tie them directly into Node 6's high-pressure steam line," Danial explained, pointing to the structural mounting pads on the deck, "the thirty-two pounds of continuous thermal head will act as a live hydraulic cushion. Every time a mortar shell hits the rock shelf above, the steam pressure in the rams will compress, absorb the energy, and push back against the kinetic impact."
Maya stared at him for two full seconds, her mind working through the complex fluid-dynamics and stress equations.
"A pneumatic shock absorber built at a macro-structural scale..." She picked up a new piece of chalk, her fingers flying across the black slate in a blur of mathematical notation. "The force-balance equation holds! The steam compression will absorb up to forty tons of downward impact load before the lead seals even begin to deform!"
"Gears!" Danial yelled, turning back toward the catwalk hoist. "Fetch the four-inch hydraulic cylinders from the old Sector 3 mine-hoist scrap pile! We're welding active steam rams straight to the ceiling!"
Three hundred yards above Sub-Level 7, at the Level 3 staging hoist in the High Glass access shaft, the air was thick with the biting reek of coal gas, hot machine oil, and raw black powder.
Captain Vane stood on the upper iron gantry, his heavy leather gauntlets resting on his sword hilt as he watched the 3rd Iron-Clad Sappers assemble their heavy artillery battery.
Four five-inch siege mortars—massive, short-barreled cast-iron pieces weighing over two thousand pounds each—were being lowered onto the upper platform by twin steel-cable winches. The sappers worked under the glare of chemical magnesium torches, their heavy leather aprons stained with axle grease and black powder residue.
"Anchor those mounting spade lugs into the granite bedrock!" Senior Sapper Commander Kren barked, his voice raspy from decades of subterranean blasting. He slammed a heavy iron sledgehammer down onto a three-inch foundation pin, driving it six inches into the stone floor. "If these bed-plates shift even a sixteenth of an inch under recoil, the shock wave will blow back up this shaft and collapse our own platform!"
A crew of six sappers, their bare torsos glistening under the harsh white magnesium light, swung sixteen-pound sledges in a rhythmic, four-count cadence: CLANG-CLANG-CLANG-CLANG. With every stroke, heavy iron expansion bolts bit deeper into the structural granite of Level 3, locking the four mortar carriages into a rigid, unyielding firing line trained directly down the vertical ventilation shaft toward Sub-Level 7.
"Commander Kren!" Captain Vane called out, descending the steel gantry stairs. "How long until your battery is layed and primed?"
Kren turned, wiping sweat from his scarred forehead with a greasy leather sleeve. "We're setting the elevation screws now, Captain. At a seventy-eight-degree downward decline, we're firing blind into the upper ceiling arch of Sub-Level 7. We aren't aiming for Vance's barricade—we're aiming for the ceiling slate above his boiler."
"Can your five-inch delayed-fuse shells breach forty feet of overhead basalt?" Vane asked, peering down into the dark, hot abyss where white-gold thermal steam whistled up through the guide cables.
"The basalt will hold," Kren answered with a cold, professional grin. "But the slate seam underneath won't. Three rounds of heavy delayed-impact powder will shatter that slate vein like dry glass. The entire upper roof arch will collapse straight down onto Node 6, and Vance's little garrison will be squashed under five hundred tons of falling rock."
"Good," Vane replied, his eyes reflecting the sharp magnesium light. "Envoy Sterling wants the battery ready by dawn. When those guns open fire, I want no gaps in the bombardment sequence."
Down in the subterranean staging yard of Sub-Level 7, Gears and four miners hauled the heavy four-inch iron cylinders back to the main deck using a heavy wooden hand-cart.
The steel cylinders were thick-walled, six feet long, and capped with heavy cast-bronze pistons designed for deep-shaft lifting. They were covered in rust and dried grease, but the internal bores were clean, protected by heavy brass end-caps that had kept out the subterranean moisture.
"Get the portable oxy-acetylene torch!" Gears shouted to Tommy. "We need to burn off these mounting flanges and cut three-inch thread entries into the lower base plates!"
For the next four hours, Sub-Level 7 became an inferno of sparks, blue welding flames, and the rhythmic CLANG-CLANG-CLANG of sledgehammers shaping structural iron brackets.
Danial worked suspended forty feet in the air on a wooden bosun's chair, his safety harness strapped to the upper crane rail. With a heavy welding torch in his hand, he fused the upper iron shoes of the hydraulic rams directly to the slate ceiling anchor pins. Sparks rained down like golden fire over the deck below, illuminating the thick smoke that gathered near the roof line.
Below him, Maya monitored the pressure manifold, adjusting the small needle valves that fed live steam from Node 6 into the newly installed ram cylinders. With every turn of her brass wrench, the heavy iron pistons extended upward with a deep, authoritative HISSS-LOCK, their bronze shoes pressing hard into the dark slate seam above.
The entire rock ceiling seemed to settle under the force, taking on a rigid, pre-stressed tension that locked the upper vault into a single, unified mass of stone and pressurized iron.
"Ram number three is pressurized to thirty pounds!" Maya shouted up to Danial, her hand resting on the manifold gauge. "Line head is stable! The ceiling anchor is fully seated!"
"Bring up number four!" Danial called down, wiping his sweat-stung eyes with his sleeve. "We have less than twelve hours before Sterling's sappers complete their battery platform on Level 3!"
By the time the final hydraulic ram locked into place, the northern bulkhead door was no longer just a single iron plate set in stone. It was backed by a massive, twelve-foot-thick composite barricade constructed of interlocking structural steel I-beams, iron-bound oak shoring timbers, and eight hundred cubic feet of dense, hand-packed salt-slag bags stacked all the way to the roof line.
Two high-pressure two-inch steam hoses were mounted through armored gun-ports cut directly into the steel frame, connected directly to Node 6's primary manifold—ready to release six-hundred-degree superheated vapor down the narrow access tunnel at the simple pull of a single bronze quarter-turn valve.
Danial unbuckled his safety harness and descended the rope ladder to the deck plates, his boots hitting the iron floor with a heavy, leaden thud.
He stood beside Maya and Gears, looking up at the four steam-pressurized hydraulic shores bracing the roof, then back toward the massive steel barricade sealing the northern gate. Sub-Level 7 was no longer a defenseless boiler room; it was an iron-ribbed, steam-powered redoubt anchored into the deep bedrock of the mountain.