$123 Million for a Submarine Two People Can Carry: Navy's Lionfish Drone Hunts Mines for 30 Hours

Two sailors. One torpedo-shaped robot. Thirty hours underwater, hunting the cheapest weapon that can sink a warship. That is the pitch behind the US Navy's Lionfish drone submarine — and on September 24, 2026, the Navy backed it with a $123.4 million production contract to HII. It is a remarkable amount of money for a vehicle small enough to be carried by hand, and understanding why the Navy is paying it tells you a great deal about where undersea warfare is heading.

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The Contract: $123.4 Million, Delivered by December 2027

The award is a firm-fixed-price modification to an existing HII contract, exercising production options for Lionfish vehicles plus the support equipment that goes with them. In plain terms, this is not a research grant or a prototype experiment — it is the Navy buying production hardware, at a fixed price, on a delivery schedule.

The contracting authority is the Naval Sea Systems Command. The work will be performed overwhelmingly in one place: about 99 percent in Pocasset, Massachusetts, where HII's unmanned systems business is based, and about 1 percent in Hampton, Virginia. Everything under this modification is scheduled to be complete by December 2027.

The funding mix is worth a look, because it shows how broadly the program is supported inside the budget. The bulk — roughly $114.5 million — comes from fiscal 2025 Navy procurement money, the account used to buy fielded equipment. Around $4 million comes from research and development funds, and about $4.8 million from Guard and Reserve equipment accounts. When a program draws procurement money at that scale, it has crossed the line from experiment to inventory.

What Exactly Is the Lionfish?

Lionfish is the Navy's name for the REMUS 300, built by HII's Mission Technologies division. The REMUS family has been working underwater for decades in research, commercial and military roles, but the 300 was designed around a specific military idea: a serious unmanned underwater vehicle (UUV) that does not need a serious ship to launch it.

The vehicle is torpedo-shaped and genuinely man-portable. Two people can carry it, and it can be hand-launched from a small boat, a pier, or the deck of almost any vessel. That sounds like a minor convenience. Operationally, it is the whole point. A mine-hunting robot that needs a dedicated mothership can only be in one place. A robot that two sailors can launch from a rigid inflatable can be in twenty places on the same morning.

The second defining feature is its modular, open architecture. The payload sections can be swapped, so the same basic hull can carry different sensor packages for different jobs. Open architecture also means the Navy is not locked into one vendor's black box for every future upgrade — new sensors and software can be integrated as they mature, which is one reason the program has moved unusually fast.

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The Numbers: Three Variants, One Hull Philosophy

The REMUS 300 is built around a hull of roughly eight inches in diameter, and it is offered in three length-and-endurance configurations. Longer hull, more energy, more time on task — the trade is weight, and even the heaviest version stays within two-person carry limits.

• Standard variant — about 80 inches long, roughly 107 pounds, around 10 hours of endurance.
• Extended variant — about 94 inches long, roughly 129 pounds, around 20 hours of endurance.
• Long-range variant — about 104 inches long, roughly 155 pounds, up to 30 hours of endurance and a range of up to about 165 kilometres.

All versions are rated to dive to 305 metres — 1,000 feet — well beyond the depth at which divers can work safely and far enough down to survey the seabed approaches to ports, straits and amphibious landing areas. Top speed is the one number where sources genuinely disagree: some list about 4 knots, others 5 knots, depending on configuration and conditions. Either way, this is not a sprinter. It is an endurance surveyor, and in mine hunting, patience beats speed — a slow, methodical sonar sweep finds mines that a fast pass misses.

Set those figures against the job. A naval mine can cost a few thousand dollars. The ship it can disable costs billions, and clearing a mined strait with crewed vessels and divers is slow, dangerous work measured in days. A 155-pound robot that sweeps for 30 hours, comes back, swaps batteries and sensors, and goes out again changes the arithmetic of that entire problem.

One Robot, Six Jobs

Mine countermeasures are the headline mission — the role Lionfish was bought for first. But the Navy's own mission list for the vehicle is much wider:

• Mine countermeasures — finding and classifying mines so they can be avoided or neutralised, without putting a crewed ship in the minefield.
• Intelligence, surveillance and reconnaissance (ISR) — quietly watching harbours, approaches and coastlines.
• Anti-submarine warfare support — listening and sensing in waters too shallow or too risky for larger platforms.
• Electronic warfare — carrying electronic payloads into contested littoral zones.
• Search and recovery — locating objects on the seabed, from lost equipment to downed aircraft wreckage.
• Hydrographic survey — mapping the seabed in detail, the unglamorous work that every amphibious and undersea operation quietly depends on.

That multi-mission flexibility is exactly why small UUVs are proliferating across the fleet — and why the industrial base behind them is expanding on land as well as at sea, as we reported in our look at Anduril's new submarine factory plans. The Navy is building an undersea robot ecosystem, not a single gadget.

Replacing the Swordfish — and a Program That Moved Fast

Lionfish replaces the Mk 18 Mod 1 Swordfish, the Navy's earlier small UUV, which was based on the smaller REMUS 100. The step up matters: more endurance, more payload, deeper diving, and a modular design the older vehicle never had.

The program's timeline is unusually brisk by Pentagon standards. The REMUS 300 was selected in 2022. The first production contract followed in September 2023, covering nine vehicles. The options in the contract structure could take the fleet as high as 200 vehicles, with a total program value above $347 million if all are exercised. This latest $123.4 million modification is the sound of those options being converted into real hardware.

HII describes Lionfish as the Navy's first program to move from an other-transaction prototype agreement all the way to full production, and describes the REMUS 300 as the Navy's only cyber-compliant UUV. Those are the manufacturer's claims, and we attribute them as such — but even discounting the marketing, the observable facts support the core story: selection to production contract in about a year, and a nine-figure production modification three years after that.

Why It Matters

Three reasons. First, mines are the Pacific problem nobody can wish away. In any serious conflict over Taiwan or the South China Sea, mines would be among the first weapons used and the hardest to clear. Every Lionfish delivered is clearance capacity that does not risk a crew.

Second, the cost curve finally favours the defender. Mine warfare has always been asymmetric in the attacker's favour — cheap mines, expensive clearance. A portable, mass-producible robot that any unit can launch attacks that asymmetry directly. Two hundred vehicles, if the Navy exercises all its options, is not a niche capability; it is a distributed mine-hunting network.

Third, portability is a strategy, not a spec-sheet detail. Because Lionfish needs no dedicated ship, it can operate from allied ports, expeditionary bases and vessels of opportunity across the Indo-Pacific. That complicates an adversary's planning far more than a handful of exquisite, ship-bound systems ever could.

Frequently Asked Questions

How much did the Navy's Lionfish contract cost?

The September 24, 2026 modification is worth $123.4 million, covering production vehicles and support equipment, with work due to finish by December 2027. If the Navy exercises all options in the wider program, the total could exceed $347 million for up to 200 vehicles.

How long can the REMUS 300 stay underwater?

It depends on the variant: roughly 10 hours for the standard version, 20 hours for the extended version, and up to 30 hours — with a range around 165 kilometres — for the long-range version. All variants can dive to about 305 metres (1,000 feet).

What does the Lionfish replace?

It replaces the Mk 18 Mod 1 Swordfish, the Navy's previous small UUV based on the REMUS 100. Lionfish offers longer endurance, greater depth, more payload capacity and a modular open architecture the Swordfish lacked.

Why does mine hunting need a robot at all?

Because the alternative is sending crewed ships and divers into a minefield. Mines are cheap, plentiful and patient; a portable UUV can search for them for hours at no risk to human life, and can be launched from almost any small craft.

Our Take

The Lionfish will never be the most dramatic vehicle in the Navy's arsenal — it has no weapons, no speed record, no silhouette for a recruiting poster. But wars at sea are often decided by the unglamorous arithmetic of who can open a strait, clear a harbour approach, and keep shipping moving. A $123.4 million bet on a submarine two people can carry is the Pentagon quietly admitting that the future of mine warfare is small, cheap, numerous and uncrewed. The mine has been the poor navy's great equaliser for a century. Lionfish is what it looks like when the rich navy finally builds an equaliser of its own.

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