The United States Navy has test fired a pair of Tomahawk cruise missiles from USS North Dakota (SSN-784), the first Block III Virginia-class submarine.

Unlike previous Virginia-class SSNs, the Block III version dispenses with 12 individual tubes for cruise missiles and replaces those with a pair of large diameter Virginia Payload Tubes.

With the new configuration, each VPT will carry six missiles in a canister that can be swapped out—but the new system initially had some teething issues. Those issues have been resolved, leaving the Navy with a launch system with few parts and which should be more reliable while also allowing for future growth.

"As the Navy continues to modernize its subs, Raytheon continues to modernize Tomahawk, keeping this one-of-a-kind weapon well ahead of the threat," Mike Jarrett, Raytheon Air Warfare Systems vice president, said in a statement.  

"Today's Tomahawk is a far cry from its predecessors and tomorrow's missile will feature even more capability, giving our sailors the edge they need for decades to come."

The VPT is in some ways the harbinger of the future.

The Navy is currently developing the Virginia Payload Module (VPM), which would add a roughly 84-foot hull section to the Virginia-class boats containing four 87-inch missile tubes. Each of those four tubes could then carry seven additional Tomahawk cruise missiles in Multiple-All-Up-Round Canisters (MACs). That would afford each submarine the capacity to carry 28 additional Tomahawks—bringing total missile capacity up to 40 weapons. In the future, those tubes could be used to carry different payloads.

The VPM will be added to the Virginia-class boats starting in fiscal year 2019 starting with the second Block V vessel are ordered that year. All subsequent Virginia-class vessels would incorporate the VPM module, which is needed to compensate for the retirement of four Ohio-class ballistic missile submarines that were converted into SSGNs.

The Navy hopes to sustain building two SSNs per year even during the years where it must build new Columbia-class ballistic missile submarines to replace the aging Ohio-class boomers, but the service is studying the possibility of building three Virginia-class boats per year in during the years when its not buying SSBNs.

A recent Navy report to Congress states that building two SSNs and an SSBN per year is feasible—which would give the service seven additional boats by 2030. But even seven boats will not help the service meet its revised requirement for 66 attack submarines. Seven boats will only help to arrest the fleet’s decline—which is forecast to shrink to only 41 boats by 2029.

The Navy is likely going to have to build at least three SSNs per year for the foreseeable future if it has any hope of meeting that requirement. In fact, the Navy might have to build more than three SSNs per year to close the gap in a timely fashion.

The demand for submarines is only going to become more intense as Russia and China continue to challenge the United States in the undersea domain.

Dave Majumdar is the defense editor for The National Interest. You can follow him on Twitter: @Davemajumdar.