by DAVID AXE

For several years now the U.S. Navy has been planning to replace older attack and cruise-missile submarines with an improved version of the cutting-edge Virginia-class undersea boat. And in late October, Adm. David Johnson, the sailing branch’s top sub-builder, finally unveiled the new vessel’s possible configurations during a conference in Virginia.

Options for the so-called “Block V” Virginias range from a nearly 480-foot-long behemoth to a simpler model that’s just 450 feet from bow to stern. But all five proposed designs are longer than today’s standard Virginias, which measure just 380 feet.

And for a good reason. The Block Vs—the Navy wants to build 10 of them between 2019 and 2023—are expected to include a structural plug, known as a “payload module,” inserted in the middle of the standard nuclear-powered Virginia design. The module is meant to accommodate four vertical tubes that open to the water and can be accessed from inside the ship.

These payload tubes could carry sea-launched robots, divers or—most significantly—seven Tomahawk cruise missiles apiece. Combined with the six-round tubes already installed in the bow of a standard Virginia, a fully missile-loaded module would boost a sub’s Tomahawk count to an impressive 40 missiles. Each maneuverable, GPS-guided Tomahawk can fly a thousand miles at low level and hit a target with pinpoint accuracy.

The Navy wants the missile-heavy Block V subs to replace the current fleet of four dedicated cruise-missile submarines. The SSGNs, as they’re known, were modified in the early 2000s from surplus “boomer” boats carrying nuclear-tipped ballistic missiles. Each SSGN packs up to 154 Tomahawks. In 2011 the USS Florida cruise-missile sub fired at least 90 Tomahawks at targets in Libya, clearing the way for follow-on attacks by warplanes.

The SSGNs are all already nearly 30 years old and will retire in the mid-2020s, resulting in a precipitous decline in the Navy’s overall cruise-missile capacity. A force of 10 Block V Virginias would make up for around half of the missile shortfall. Subsequent Block VI and Block VII submarines could restore the other half.

General Dynamics Electric Boat in Connecticut, the Navy’s main submarine-builder, sketched out a basic, 94-foot payload module a few years ago. Last year, amid worsening budget uncertainty, the module options ballooned to five.

The longest three—97, 91 and 88 feet—differ in their precise layout and the number of new bulkhead walls they add to the baseline Virginia design. But they all preserve the sub’s 34-foot-diameter outline, “allow[ing] the platform to perform within key performance parameters,” according to Electric Boat vice president John Holmander

Two shorter and simpler options with 70-foot module plugs include humps on the sub’s hull allowing for slightly taller and therefore more voluminous tubes. But this “turtleback” arrangement comes with “attendant hydrodynamic and potential acoustic problems, especially at the higher speeds,” retired Capt. Karl Hasslinger and John Pavlos wrote in the Navy’s official Undersea Warfare magazine.

It’s costing $500 million just to develop the Block V design. Today’s Virginias cost slightly more than $2 billion apiece to build—and with the Block V module that unit price could rise by hundreds of millions of dollars. Whichever Block V layout the Navy chooses in coming years, it won’t come cheap.

But new submarines are among the sailing branch’s top priorities—and rightly so. Stealthy and heavily armed, undersea boats are by far the most powerful warships for full-scale warfare. With their planned extensions and more missiles, the Block V subs could be the deadliest yet.

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