When the Navy retired its last aged battleship in 1992, it pledged to the Marine Corps that it would continue fulfilling one of the warships’ missions: naval gunfire support for troops ashore. More than a quarter of a century later, and after more than a billion dollars spent, the service’s intended replacements — rocket-assisted GPS-guided shells — have yet to materialize.

The effort has been marked by a string of technological disappointments. Rocket motors failed to ignite. Guidance fins wouldn’t pop out. Antennas couldn’t acquire satellite signals before shells smashed to the ground. In decades of testing, the Navy has been unable to build replacement weapons that reliably worked, much less at an affordable price. This research-and-development failure has resulted in 36 new warships with advanced deck guns, but not the specialized munitions they were designed to fire. The Navy intends to commission 13 more ships the same way and has no immediate plan or clear option for fulfilling its promise to the corps.

Officials at the Marine Corps’ Combat Development Command in Quantico, Va., where the service sets its weapons requirements, said the Navy’s current gunfire shortfalls pose a “significant risk” to amphibious attacks, which at one time required artillery that can reach an adversary’s shore from 40 nautical miles away to support invading forces. The Navy’s current deck guns can only fire as far as 13 nautical miles.

The Government Accountability Office has periodically raised questions about why the Navy has not fulfilled its commitment. A 2006 G.A.O. report pointed to the Navy and Marine Corps’ inability to agree on what their naval surface fire support requirements should be for more than a decade, and to the Navy setting unrealistically low cost estimates for its proposed rocket-assisted guided shells. Additionally, defense analysts point to the Navy’s prioritization and funding of newer technologies — notably precision-guided munitions from aircraft — over naval gunfire. “Priorities in one space can have a chain effect and drive up costs in another program,” making it untenable, said P.W. Singer, a strategist and senior fellow at the New America Foundation. “The Navy would say it takes naval gunfire seriously, and the Marines would say, ‘Not seriously enough,’ and the two will never agree.”