Marine Corps Amphibious Combat Vehicle (ACV): Background and Issues for Congress [Updated July 23, 2020] [open pdf - 1MB]
From the Summary: "On January 6, 2011, after spending approximately $3 billion in developmental funding, the Marine Corps cancelled the Expeditionary Fighting Vehicle (EFV) program due to poor reliability demonstrated during operational testing and excessive cost growth. Because the EFV was intended to replace the 40-year-old Amphibious Assault Vehicle (AAV), the Pentagon pledged to move quickly to develop a 'more affordable and sustainable' vehicle to replace the EFV. The Amphibious Combat Vehicle (ACV) is intended to replace the AAV, incorporating some EFV capabilities but in a more practical and cost-efficient manner. In concert with the ACV, the Marines were developing the Marine Personnel Carrier (MPC) to serve as a survivable and mobile platform to transport Marines when ashore. The MPC was not intended to be amphibious like an AAV, EFV, or the ACV but instead would be required to have a swim capability for inland waterways such as rivers, lakes, and other water obstacles such as shore-to-shore operations in the littorals. Both vehicles were intended to play central roles in future Marine amphibious operations. On June 14, 2013, Marine leadership put the MPC program 'on ice' due to budgetary pressures but suggested the program might be resurrected some 10 years down the road when budgetary resources might be more favorable."
CRS Report for Congress, R42723
Congressional Research Service: https://crsreports.congress.gov/