The Virginia-class attack submarine, the SSN-774 class, came out of the cost shock of the Seawolf, a $2.8 billion boat built to hunt Soviet submarines and canceled after three hulls once the Cold War ended. The Navy’s Two for Four goal sought two boats for $4 billion by fiscal 2012. Only two U.S. yards are certified to build nuclear submarines, General Dynamics Electric Boat in Connecticut and Newport News Shipbuilding in Virginia, and each Virginia is split between them: one builds the bow, sail and torpedo room, the other the reactor plant and engine room, and the sections travel by barge for final assembly. Each boat takes about 9 million labor hours and parts from over 4,000 suppliers, and the split keeps both yards’ welders and nuclear pipe fitters employed.

The traditional periscope is gone. Photonics masts outside the pressure hull carry cameras, infrared sensors and laser rangefinders, and the control room moved down to a roomier deck, where crews steer the masts with a standard Xbox 360 controller that can be swapped for a new one at about $30. An open architecture brings hardware refreshes every four years and software every two. The S9G reactor produces 40,000 shaft horsepower and its core is designed to last the boat’s full 33 years. Block 5 adds the Virginia Payload Module, a 70-foot section that stretches the boat from 377 to 460 feet and over 10,000 tons, raising Tomahawk capacity from 12 to 40 to replace retiring Ohio-class SSGNs. Under AUKUS, Australia is buying three used Block 4 boats, with an option on two more.

• A BAE Systems pump jet in a shrouded duct delays cavitation, the popping vapor bubbles that passive sonar listens for.
• Block 3 swapped the air-backed spherical sonar for a water-backed Large Aperture Bow array with fewer hull penetrations.
• Early boats had 12 vertical launch tubes, and Block 3 moved to two large Virginia Payload Tubes.
• The stretched Block 5 hull trades some agility for firepower, and later boats are slated for Conventional Prompt Strike hypersonic missiles.
• The Australian boats are a stopgap to replace diesel Collins-class submarines until the new SSN-AUKUS design arrives.