Navy Next-Generation Attack Submarine (SSN[X]) Program: Background and Issues for Congress [Updated September 29, 2021] [open pdf - 613KB]
From the Introduction: "The Navy wants to begin procuring a new class of nuclear-powered attack submarine (SSN), called the Next-Generation Attack Submarine or SSN(X), in FY2031. The SSN(X) would be the successor to the Virginia-class SSN design, which the Navy has been procuring since FY1998. The Navy's proposed FY2022 budget requests $98.0 million in research and development funding for the SSN(X) program. An issue for Congress is whether to approve, reject, or modify the Navy's funding requests and acquisition strategy for the SSN(X) program."
CRS In Focus, IF11826
Congressional Research Service: https://crsreports.congress.gov/