STYX

Mission

Banshee

Put ordnance, sensors and a launch-and-recovery deck on a hull cheap enough to lose, in enough places at once that no single one is worth a missile.

One STYX is a picket, and that is not the point. Six STYX on a 240-nautical-mile barrier at forty-mile spacing, each holding eight BANSHEE and four POLTERGEIST-150, is 48 interceptors and 24 cruise missiles distributed across 240 miles of ocean with no node worth a missile. The magazine is the formation, not the hull.

There is also a systems reason this ship exists that has nothing to do with weapons. In the maritime domain the surface vessel is the gateway — the only node that can hold a satellite link, an aircraft datalink and an acoustic link to something submerged at the same moment. Without a surface vessel, an undersea picture stays undersea. STYX is the boat that carries the sea domain's data across the surface, and while it is doing that, it is also an arsenal.

46.2m² Clear mission deck between the hulls. A 62 ft monohull gives 22.

9min BANSHEE recovery to relaunch, unattended, on the compensated deck.

60d Certified unattended endurance. Everything beyond it is tankage.

$9.4M Unit cost at rate. A crewed Mk VI patrol boat is about $15M.

Parameters

STYX MUSV-4 — principal characteristics
Class	Medium autonomous surface vessel — arsenal configuration
Length overall	62.0 ft / 18.90 m
Beam	21.8 ft / 6.65 m — wave-piercing aluminium catamaran, B/L 0.35
Draft	4.6 ft / 1.40 m hull; 6.2 ft with the transducer trunk lowered
Lightship	31.4 t — 5083/5383 marine aluminium
Full load	48.6 t — fuel 9.6 t, payload 6.4 t, stores 1.2 t
Clear mission deck	46.2 m² between the hulls, 4.9 t/m² over the strong points
Mission cells	12 × quarter-TEU (1.2 m cube) on a 1.25 m rail grid, each with 28 VDC, 400 VAC and fibre
Sprint speed	28.0 kt on 2 × 720 kW MTU 8V2000 M96
Loiter speed	4–11 kt on a 40 kWe genset driving a 65 kW PTI motor, mains declutched and cold
Silent approach	5 kt for 45 min on a 210 kWh LFP pack
Fuel-limited range	6,400 nm at 8 kt
Certified unattended endurance	60 days — set by machinery run certification, not by tankage
Sea state, transit	SS4 at any speed; SS6 at 12 kt
Sea state, survival	SS8 / 12 m significant wave height, unattended autonomous heave-to
Sea state, BANSHEE recovery	SS4 routine; SS5 with roughly a 30 % wave-off rate. Launch SS5.
Sea state, SHADE ops	SS5
Sensors	360° panoramic EO/IR (8 × 5 MP visible + 4 × 640 LWIR, 1.1 mrad), solid-state X-band nav radar 0.8 m, ESM, AIS, two hull hydrophones
Comms	REVENANT MESH: line-of-sight optical 40 Mbps at 14 km with zero RF emission; HF and UHF fallback; acoustic modem to submerged nodes; REVENANT LINK to Link 16, TTNT and IBCS
Autonomy	REVENANT CORE plus the declarative COLREGS engine
Crew	0 — no accommodation, no galley, no head, no helm station
Delivery transit	Autonomous under a filed voyage plan; no delivery crew, no chase boat
Boarding provision	Recovery harness and a towing eye. The boat is not designed to be gone aboard at sea.
Unit cost target	$9.4M at rate

Mission deck capacity
BANSHEE-M / -R	8 — six in the magazine, two in deck cells
SHADE-M / -R	24 in two 12-round tube launchers
POLTERGEIST-150	4 canisters in deck cells
TIDEWALL nodes	12-node laying spread, over-stern chute
Launch	1 × 2.4 t uncrewed surface tender and davit — laying, recovery and inspection
Autonomous weapon station	1 × 30 mm, bow cell — cued by the boat, released under LEDGER-signed authorization
Reconfiguration	Under 4 h pierside on the rail grid

Landing an aircraft on a 62-foot boat

01 · The problem

BANSHEE's entire economic argument is that if it does not engage, it comes back. That argument evaporates if it can only come back to a pier.

Recovering a VTOL onto a 62-foot boat in sea state 4 means putting it on a deck that is heaving 1.4 m, rolling 8 degrees and pitching 5, with a deck-relative closure that has to be resolved in the last two metres. "Land on the deck and hope" does not survive a real Pacific afternoon.

02 · Compensate the deck

A 3.2 × 3.2 m six-degree-of-freedom Stewart platform is set into the mission deck: ±0.90 m of heave authority, ±12° roll, ±8° pitch, 380 mm/s actuator slew, closed at 200 Hz on the vessel's own motion reference unit. In sea state 4 it holds the landing surface to ±0.6° and ±80 mm. It weighs 2.1 t and draws 22 kW peak, 3 kW average.

Feed-forward matters more than the actuators. A hexapod chasing measured motion is always one phase behind the sea. A hexapod driven by a 1.1-second wave prediction from the forward-looking X-band radar and the motion reference unit stays ahead of it, and 1.1 seconds is enough.

03 · Capture, don't land

At the centre of the platform is a 1.1 m compliant capture ring with four claws. BANSHEE flies a 1.5 m/s descent to a three-metre relative hover on relative GNSS and an optical fiducial pattern, then commits. On weight-on-skids the claws close in 220 ms.

The aircraft is never asked to make a soft landing on a moving surface. It is asked to be inside a 1.1-metre circle for a quarter of a second. That is a far easier problem, and it is the one the whole deck is designed around.

The platform then indexes down through a deck hatch into a magazine and service bay, where a two-axis manipulator swaps the battery, refuels, and re-arms from a 12-round effector rack. Nine minutes, unattended.

04 · Where it stops

Recovery is sea state 4 routine and sea state 5 with roughly a 30% wave-off rate. Launch is sea state 5. Above sea state 5, STYX is a sensor and a communications node, not an airfield, and the BANSHEEs it launched had better have somewhere else to go.

COLREGS is a legal problem, not a path-planning problem

Collision avoidance is not path planning. It is a legal problem with a path-planning component, and treating it as the former is why unmanned surface vessels are still shadowed by a chase boat with a licensed mariner aboard.

Rules 13 to 17 — overtaking, head-on, crossing, give-way action, stand-on action — are geometry, and geometry compiles. Rules 2, 5, 6, 7, 8 and 19 are judgement, and judgement is what gets litigated. The worst of them is Rule 17, which requires the stand-on vessel to act when it becomes apparent that the give-way vessel is not taking appropriate action. That is a machine deciding a human mariner is failing, and then overriding him. There is no way to write that rule without writing an opinion.

So we sign the opinion. The COLREGS engine is a declarative rule set inside REVENANT CORE, and every avoidance manoeuvre is LEDGER-signed together with the contact picture that justified it. After an incident the investigator receives a signed, replayable record: which contacts were held, at what CPA and TCPA, which rule the engine believed governed, the moment it concluded the give-way vessel was not acting, what it did, and what the alternatives it rejected would have cost. No other USV can produce that record, and it is the only way a flag state, an insurer or an admiralty court can treat an unmanned vessel as anything other than an unattributable hazard.

Autonomous navigation — behaviour and acceptance
Rule 5 — look-out	Panoramic EO/IR detects an unlit 6 m hull at 2.9 km and a floating container at 900 m. Radar holds a 5 m² target at 8 nm in SS3. And two hull hydrophones — Rule 5 says "by sight and hearing", and we hold ourselves to both halves of it. STYX hears a fog signal and an approaching screw.
Rule 3(g) / Rule 18	While operating BANSHEE the vessel is restricted in her ability to manoeuvre, and displays the lights and day-shapes that say so. That is not decoration — under Rule 18 it obliges power-driven vessels to keep clear while the deck is hot.
Rule 8(b) — manoeuvre policy	Large and early: a 30° course change at 6 nm, not a 5° nudge at 2 nm. An alteration must be "readily apparent to another vessel observing visually or by radar." A mathematically optimal micro-correction is legally indefensible and illegible to the mariner it is aimed at. We give up efficiency to be readable.
AIS and running dark	AIS receives always and transmits by default. Going dark is a commanded state entered only on a LEDGER-signed authorization naming the human who ordered it and the window it is valid for.
CPA envelope	0.5 nm open ocean · 200 m in a traffic separation scheme · 60 m in a harbour approach at 6 kt or less
Acceptance gate	Zero COLREGS violations across 14,000 nm of witnessed trials in Class A and B traffic, adjudicated by licensed masters reviewing the signed record

CONOPS

Phase 01 · Sortie

Any pier, any well deck, under its own power

No launch equipment, no crane, no mother ship. The mission deck is reconfigured pierside in under four hours on the rail grid, which means the boat that sailed as a counter-UAS picket comes back as a seabed-laying platform without going near a shipyard.

Phase 02 · Transit

8 kt on the loiter drive, mains cold

AIS transmitting, lights and shapes correct, COLREGS engine holding a half-mile CPA envelope. 6,400 nm of fuel available; 60 days certified. The main engines are not started for a transit — running a 720 kW diesel at 26 horsepower destroys it, which is the entire reason the loiter drive exists.

Phase 03 · Barrier establish

Forty-mile spacing, one picture

Optical mesh to neighbours comes up at 40 Mbps with zero RF emission. Emissions go receive-only. An acoustic handshake reaches any LEVIATHAN or TIDEWALL field beneath, and the barrier becomes the surface end of the undersea network.

Phase 04 · Persistent watch

Radar, EO/IR, ESM, passive acoustic — fused and signed

Every contact goes into one barrier-wide picture, hash-chained at the edge. SHADE is launched for close-look identification of contacts the radar cannot resolve, at four pounds a copy.

Phase 05 · Engage

On a signed token, and any hull can shoot on any hull's track

BANSHEE against air and cruise threats, POLTERGEIST against surface and land targets. Engagement authority is a LEDGER capability token that is issued once and consumed once — there is no ambiguity about who authorized a shot and no mechanism by which two hulls service the same target twice. Unexpended BANSHEEs come home to the compensated deck and regenerate a sortie in nine minutes.

Phase 06 · Sustain

Any vessel with a five-tonne crane

Deck cells are replenished at sea from whatever is available, or the boat returns to any pier. There is no specialised tender in this concept, because a specialised tender is a coordinate and a single point of failure.

Phase 07 · Withdraw or scuttle

It is a $9.4M object

If the boat cannot be recovered, its data has already gone out over the mesh and the hull is scuttled on a signed authorization. Nothing about the campaign plan depends on getting any particular hull back.

Why it is built this way

The mission deck is the product, and the mission deck is why this is a catamaran. A 62-foot monohull gives roughly 22 m² of usable working deck. A wave-piercing catamaran of the same length gives 46.2, because the deck spans the tunnel. It also has far better roll behaviour in short seas — which is what actually governs whether you can land an aircraft on it — and two widely separated shaft lines, so a single-engine casualty is a limp-home rather than a tow.

Everything else follows. The hybrid drivetrain exists because a 60-day boat cannot run its sprint engines at 4% load. The wave-compensated platform exists because reusability is worthless if the aircraft can only come home to a pier. And the COLREGS engine is declarative and signed because an unmanned vessel that cannot explain itself after a collision will never be allowed out of sight of a chase boat.

The argument · arsenal ship

An arsenal ship is not an attack craft — and the deck is what makes the difference

An attack craft measures combat power in rounds carried. An arsenal ship measures it in sorties per day. A hull that carries effectors to a place and expends them is finished when the cells are empty, and every hour after that it is a fast boat steaming toward a pier. STYX is built the other way round: the modular mission deck launches and recovers BANSHEE and SHADE at sea, so a round that is not spent comes back, refuels and flies again. A six-hull barrier reloads itself.

The deck is the whole argument. A 3.2 × 3.2 m Stewart platform driven by a 1.1-second wave prediction holds the landing surface to ±0.6° and ±80 mm in sea state 4 — which is what turns recovery at SS4 and launch at SS5 into a scheduled evolution rather than a stunt. Nine minutes from touchdown to relaunch, unattended, with nobody on deck. Remove the platform and STYX is a magazine with a hull under it.

Built organically on our own quay. STYX is designed, fabricated, outfitted and launched at FORGE-1 on Fantom's own deepwater quay in Savannah. The hull, the autonomy, the mission deck and the production rate sit inside one organization, so the schedule is ours to hold and the hull reaches water at the fence line — which matters for a 48.6 t vessel that cannot be trucked.

Where the program actually stands: STYX is in detail design, with trials in 2029. The figures on this page are design targets, tank-test results and calculations — not sea-trial data — and we present them as such.

FORGE-1 and the outfitting quay

What is hard, stated plainly

Open engineering risks — STYX
Unattended machinery reliability	This is the whole program. A crewed boat has an engineer who notices a weeping seal at 0300. Sixty unattended days means the boat diagnoses itself — 340 sensed points and a vibration-signature model per rotating machine. First-year MTBCF target is 1,400 h. The mission needs 2,600 h. We are not there and we know exactly how far.
The compensated platform	2.1 t of hexapod exposed to green water, salt and thousands of cycles per deployment. The failure mode is graceful — it locks level and reverts to a fixed deck — but recovery then drops to SS2 and BANSHEE's reusability argument collapses with it.
Not self-righting	Stated above rather than engineered around.
Fouling	Sixty days at 6 kt in warm water costs about 22 % of speed by day 60 in the Gulf. Foul-release coating helps. A hull-crawler would fix it. We have not built the crawler.
Regulatory	Flag-state and classification treatment of a 48 t unmanned vessel is unsettled. We build to ABS autonomous-vessel guidance and DNV's ARV rules and fully expect both to change underneath us mid-program.
Weapon release policy	Whether an unmanned surface vessel may fire in peacetime waters is a policy question we do not get to answer. The LEDGER token architecture is built to make it answerable. That is not the same as answered.

Related systems

All sea systems

Banshee Eight rounds aboard. The nine-minute turnaround is measured on this deck, with nobody standing on it.

Shade Twenty-four in two tube launchers. Recovery into a soft catch cone is trivial at 4.1 lb.

Leviathan The thing on the other end of the acoustic link, 400 m down.

Government & Primes

Request a STYX briefing

Mission-deck interface control documents, the COLREGS engine's rule set and trial adjudication plan, and barrier-concept modelling are available to US government customers and allied ministries of defence under an executed agreement.

Request a briefing programs@fantom.aero

Every figure on this page is a design target derived from first-principles analysis, not a trial result. STYX is in detail design; sea trials are planned for 2029. No export-controlled information is published on this site.