The Baric Back-Draft

Cold grease froze faster where the hull projected over the central shaft. On the forward sponson of the Kasumi-maru, sixty fathoms of void whistled through the scuppers, dragging salt spray and coal smoke down into the drop-throat. Bombardier Captain Tomoki wiped a dollop of sheep tallow across the starboard mortar’s touch-hole, watching the aneroid needle on the carriage casing shudder against its brass pin. He needed fifty pounds of baric thrust out of an uninspected charge, or the slipway master would drop their mooring hooks into the descent with sixty tons of dead iron they could neither steer nor brake.

Behind him, Master Gunner Masato knelt beside a brass-hooped bucket. Inside lay six pounds of propellant scooped from an unbroached barrel in Rack Five, sealed in boiled parchment to keep the damp out. The gray granules did not smell like charcoal and nitre; they gave off the sharp, briny stink of squid marrow gone sour in the sun.

"The needle sits at twenty-four baric notches," Masato growled, his hand resting on the wooden lever of the carriage elevation wedge. His deaf ear was turned toward the open shaft, his whiskers stiff with rime. "Air is too thin out here on the rim, Captain. If deep-grade powder catches spark before we clear the upper shear, the combustion won't find enough teeth in the wind to shove outward."

"We cannot fall through two spheres with a dead battery," Tomoki said. He checked the breech threads of the sixty-pound bronze mortar. The metal was clean, honed to a mirror sheen by generations of apprentices, yet along the venting channels a faint oily glaze had already begun to separate. "If the propellant still holds its ratio, five grains will throw the test plug thirty paces into the shaft. If it refuses, we flag the slipway tower and submit to Citadel quarantine before sunset."

Masato spat over the coaming. "Quarantine means the brand-irons. Overseer Kazuma's cutters are already anchored at Waystation Four. You think they’ll fumigate the bilges with incense and hand us clean vouchers? They’ll burn the hull to the copper bolts and hang the gun-crew from the slipway gallows to keep the celestial air pure."

"Prime the pan," Tomoki commanded.

Two conscript loaders stood by the recoil balks, their hemp breeches stiff with dried bilgewater. The elder of the two, a thick-shouldered conscript whose scarred knuckles gripped the rammer stave, kept his chin tucked against the draft. Neither man spoke. A naval crew learned early that junior gun-hands had no business asking why an officer ordered a muffled shot while docked at a royal berth.

Masato uncorked the horn flask. He trickled a narrow line of fine-milled priming down the vent-trough, his thick thumbs steady despite the freezing gusts rising from the abyss below. The grains tumbled into the bronze groove, gray and coarse as crushed slate.

Tomoki watched the aneroid needle. It drifted a fraction toward the low-pressure redline, trembling as a thermal downdraft peeled off the slipway's timber apron. The barometer warned of thin air, but the vent-trough displayed something far worse. The powder was not settling into a loose wedge; the grains clumped together, shivering against the bronze as if reacting to the iron of the lock. Tiny oily filaments, thin as spiders' silk, reached out from the charcoal facets toward the vent screw.

"Hold the portfire," Tomoki said.

Masato paused, the smoking matchcord poised two inches above the priming trough. "Captain?"

"Look at the trough."

A faint thread of cold green luminescence coiled along the touch-hole. It did not smolder; it seeped. The sulfur was sweating an oily fluid that coated the bronze vent plug in wet black beads.

"It took the grease," Masato muttered under his breath. "The marrow in the grain is drinking the mutton fat."

"Prime the vent," Tomoki commanded. "Keep the match away. Pull the friction lock on my count."

Masato nodded, his jaw set. He hooked the copper lanyard clip to the friction striker inside the touch-hole and backed three paces toward the bulwark, the braided cord drawn taut across his knuckles.

"Clear the carriage," Tomoki said. The hair on his forearms rose beneath his lead-wool sleeve. A high, singing tone began to vibrate through the bronze trunnions—not the solid ring of cast metal under stress, but the hollow whistle of a flue drawing air inward. "Masato, heave!"

Masato snapped his wrist. The lanyard cord jerked taut.

The striker scraped iron against flint, and the primed vent flashed.

A sudden, sharp pop snapped from the touch-hole. Instead of an orange flare and an outward plume of white sulfur smoke, a jet of violet vapor hissed backward into the vent. The aneroid glass on the carriage frame cracked with a sharp ping.

Tomoki did not shout an order. He seized Masato by the heavy leather lapels of his sea-coat and threw his full weight sideways, driving the master gunner down behind the thick white-oak recoil balk bolted to the waterway.

The mortar did not thunder. It gasped.

A concussive vacuum slammed the sponson deck. The atmosphere tore inward toward the muzzle with the sound of a collapsing sail, stripping the breath from Tomoki’s lungs in a violent rush of pressure. The sixty-pound bronze mortar bucked on its slides, its heavy iron carriage groaning as forty atmospheres of drop-shaft air attempted to jam themselves down a three-inch bore.

The bronze vent plug, sheared clean from its four-inch steel threads by the implosive suction, vanished down the touch-hole with a shriek of tortured bronze.

A terrible crack echoed across the sponson. The two conscript loaders standing at the breech had no oak beam to shield them. The baric back-implosion snatched them forward against the carriage frame with sickening momentum, crushing the elder loader's ribcage against the iron cascabel and snapping the second man's rammer stave into jagged splinters before slamming his skull into the bronze trunnion.

Both men collapsed into the waterway, tangled together in the scuppers like discarded hemp line, their chests motionless and their faces darkened by broken vessels where the baric vacuum had pulled blood into the skin.

Silence rushed back over the deck, filled only by the eternal, hollow roar of the central drop-shaft below.

Tomoki pushed himself up from the salt-crusted deck. His left shoulder throbbed where it had struck the carriage balk, and his ears rang with a shrill, deafening whine. Beside him, Masato rolled onto his knees, coughing violently and clutching his bruised ribs.

The starboard mortar sat cold in its carriage. A thick, gelatinous black sludge was bubbling slowly from the touch-hole, dripping down the bronze cascabel onto the oak planking. Where the liquid touched the iron traversing track, the metal hissed, pitted with tiny corrosive craters.

Masato spit a mouthful of blood onto his sleeve, then stared at the smashed conscripts lying by the scupper. His good ear twitched.

"Well," the old gunner wheezed, his voice raw as scraped hide. "Admiralty won't dock their rations for wasting imperial shot. Gun ate its own breech."

Tomoki stepped past the dead loaders. He did not touch their bodies; their skin was already turning an unnatural, bruised gray under the fingernails where the vacuum had ruptured the capillaries. He bent over the mortar's muzzle.

Inside the bronze bore, there was no soot. No black crust of burnt charcoal, no dry flakes of sulfur. The inner rifling was coated in a glistening, webbed membrane that pulsed with faint, dying phosphorescence. The bronze vent plug lay inside the chamber, collapsed in upon itself like a pinched pewter cup.

"It is not bad powder," Tomoki said, his voice flat and hard against the wind. "The grain did not fail to ignite. It inverted. It fed on the draft."

"Which means every mortar aboard is a suicide box," Masato whispered, hauling himself up against the bulwark. His grizzled face looked suddenly gaunt in the twilight. "We drop into the shaft tonight, Captain. When the slipway hook lets go, we have two thousand leagues of vertical void before we hit the buoyancy cushions of Echigo. If we cannot fire the anchor mortars to grab the gravity guides, we plunge straight to the trench."

"Go below," Tomoki commanded. "Check the flues on Rack Four and Rack Six. Take the copper draw-knife. Do not use an iron wedge."

Masato nodded once, wiped the rime from his brow, and ducked through the forward hatchway.

Tomoki remained alone on the sponson. Across the iron lip of the Shinano slipway, the signal lamps were beginning to flare red and amber through the gathering mist. Steam whistles wailed from the mooring towers as the evening tide of air began its downward surge into the drop-shaft abyss. In less than two bells, the harbor regulators would demand their certified trim sheet.

The forward hatch creaked open. Masato climbed back onto the deck, his breath coming in ragged, shallow gasps. His leather apron was smeared with a greasy, viscous discharge that reeked of rotting cephalopod fat and sulfur acid.

"What did you find?" Tomoki asked.

Masato held out his trembling hands. Between his palms he cradled a chunk of cedar stave pried from the lower bulkheads. The wood was soaked through, soft as wet cheese.

"It’s not just Cask 14, Tomoki," the master gunner said, dropping the formal title as his voice broke. "The entire lower tier under the keel. All three hundred anchor charges. The staves have split from the inside out."

Masato pointed a trembling finger down toward the open hatchway, where an oily, glistening trickle of black bile was already weeping through the oak deck seams into the twilight.

"They're not waiting for us to fire them," Masato said. "They're melting."