Completing the pressure hull is the last major construction milestone for the submarine before it is launched.
Huntington Ingalls Industries (HII) Newport News Shipbuilding, which is building Massachusetts, is one of two US shipyards capable of designing and building nuclear-powered submarines.
The other yard building the Virginia-class is General Dynamics Electric Boat.
Massachusetts is the 25th Virginia-class SSN for the USN.
According to Shephard Defence Insight, each Virginia-class boat has a submerged displacement of 7,925t and measures 114.8m in length.
The boats are powered by a GE PWR S9G nuclear reactor and two turbines offering an unlimited range and a maximum speed of around 25kts.
Virginia Class Attack Submarine (SSN 792-SSN 811)
Virginia Class