I don't know who at the Pentagon decided to call America's new fleet of uncrewed naval warships "Ghost Fleet Overlord." But whoever came up with the name deserves a raise, a promotion, and a job with a major advertising firm just as soon as they retire from the Navy.

For more than a decade, the U.S. Navy has been working to build a robot navy, beginning with unmanned aerial vehicles and underwater drones launched from manned warships, and later scaling up to entire autonomous warships. It's the latter we'll be talking about today -- the autonomous warships of Ghost Fleet Overlord, which sailed in all its robotic majesty into Sydney Harbour in Australia last month in a coordinated demonstration of how far America's robot navy has already come.

Pentagon watchers will want to know that this robotic fleet has grown from just one single testbed vessel seven years ago (the "Sea Hunter," America's first robot warship). It now comprises four named unmanned surface vehicles (USVs), as the Ranger, Mariner, and Seahawk have joined the fleet. Investors, meanwhile, may be more interested in knowing which defense contractors are building these robot vessels. Because it's becoming more and more obvious that the Navy likes these ships -- and wants to buy more of them.

Leidos and L3Harris (and Lockheed Martin, too)

Broadly speaking, the four USVs that arrived in Australia last month come in two flavors: 135-foot long, 145-ton trimaran vessels Seahawk and Sea Hunter, built specifically to be unmanned warships; and 194-foot long, 670-ton monohull vessels Ranger and Mariner, built as ordinary crewed vessels, and then equipped with technology to make them autonomous.

All four ships were built by privately held Gulf Craft LLC under a contract with defense company Leidos (LDOS -0.77%), which pioneered the idea of autonomous warships through contracts with the U.S. Defense Advanced Research Projects Agency (DARPA). Leidos also provides the technology -- the "brains" of the boat -- that allows three of these vessels to function as autonomous or remote-controlled warships.

The exception is the USV Mariner, which incorporates autonomous technology from Leidos rival L3Harris Technologies (LHX -1.39%). In turn, L3Harris worked with Australian shipbuilder Austal to enable the Mariner to operate autonomously.

What can these vessels do?

At present, all four ships are considered more technology demonstration projects than full-fledged fighting vessels. But over time the Navy plans to advance the concept of autonomous warships, scale up their size -- and buy a lot more of them.

For example, USNI News and the Congressional Research Service note that the Navy plans to buy nine full-scale "large USVs" or LUSVs (the current Ghost Fleet Overlord ships are considered "medium" size) through 2028. These LUSVs will be much bigger than even the biggest MUSV -- as much as 300 feet long and displacing as much as 2,000 tons -- and capable of carrying anywhere from 16 to 32 missile launchers in addition to robust radar and other sensor technology.

Speaking of which, that brings us to the third big publicly traded defense stock involved in this effort: Lockheed Martin (LMT -1.10%). As it turns out, the USV Mariner is currently equipped with a low-power Lockheed Aegis weapons system for detecting and targeting opposing warships and aircraft.

What it means for investors

So Ghost Fleet Overlord is starting to look quite robust as a weapons system, sporting both far-seeing eyes (radar) and sharp teeth (missiles), too. The next logical question is: How much will these robot warships cost -- and what kind of revenue should defense investors be anticipating?

Actually, the numbers may surprise you. Leidos's USV Sea Hunter and Seahawk, for example, cost just $55.5 million to produce -- total. Ranger and Mariner, being bigger ships, probably cost more -- but perhaps not much more.

Granted, the LUSV ships the Navy wants will probably cost quite a bit more to build. Earlier this month, the Navy laid out plans to spend an average of about $250 million per vessel across the fleet of nine LUSVs. Across all 13 ships (assuming the MUSVs remain in service), the total cost of this program still probably comes to less than $3 billion -- less than the price tag on one single model of the Navy's now-discontinued DDG-1000 destroyer. And because these vessels don't require crews, their estimated cost to operate ($15,000 to $20,000 per day) is a fraction of the cost to operate a crewed destroyer -- nearly $1 million per day.

For a budget-constrained Navy, this makes for a powerful argument in favor of buying more LUSVs. And with Leidos and L3Harris -- the two defense contractors with the most skin in this game -- selling for just 14 times forward earnings each, betting on these two stocks to profit from the new technology doesn't look risky, or expensive, at all.