What the Navy really needs are rapid firing 5” “shotgun” shells to send a hail of steel to engage incoming missiles as a last line of defense.
Something similar has existed since the late 80's. They are now on all our combat ships, IIRC. Search: Palanx (CIWS)
Similar has been around for a long time. The 105mm Behive round was commonly used during the 60s.
Isn't that what the CIWS (R2-D2) does?
They developed guided munitions with a fragmentation charge. The high-G guidance package is the enabling advancement allowing choice of the Combustion-Light-Gas-Gun over the Rail-Gun. The CLGG had consistency (ignition/combustion) issues which degraded accuracy at extremely long range with inert (dumb) rounds. The rail-gun has proved not durable under the required operating demands.
They should now revert to implementing the gas-gun for the Naval application primary weapon. The smooth bore does not suffer extreme wear upon repeated firing. The projectile achieves more than 2500 meters/second velocity. It would cost five percent to fire a smart round able to replace a $2,000,000 long range missile.