The Navy has apparently made a decision I find incomprehensible. They have decided to alter the DDG-1000 design, replacing the two 57mm Mk110 mounts (the same gun on the Bertholf class and projected for the OPC) with two 30mm Mk 46.
“The Navy has replaced two 57mm guns planned on the Zumwalt-class guided missile destroyer designed to fight off swarm boat attacks with a smaller pair of 30mm guns, Naval Sea Systems Command (NAVSEA) told USNI News on Monday.”
“A follow on 2012 assessment using the latest gun and munition effectiveness information, concluded that the MK46 was more effective than the MK110 CIGS. Based on that assessment, approval was received to change from the MK 110 CIGS to the MK 46 Gun System. In addition to the increased capability, the change from MK110 to MK46 resulted in reduction in weight and significant cost avoidance, while still meeting requirements. DDG 1000 is planned to have two medium range MK46, 30mm Close-in Gun Systems that will provide a robust rapid fire capability and increased lethality against hostile surface targets approaching the ship.”
The Mk 46 mount uses the Mk44 30mm chain gun that is derived from the same 25mm chain gun used in the Mk38 mounts. It looks like a small tank turret, but I understand it is not armored. It can be remotely controlled or manned by an on mount operator.
Comparing the two weapons,
Range of the 57mm is four or five times the range of the 30mm.
Projectile weight of the 57mm is about six times that of the 30mm.
Rate of fire is similar, 220 for the 57mm and 200 to 250 for the 30mm.
The only advantage I see for the 30mm is that it has more ready ammunition on the mount (not sure how much but apparently at least twice the number of rounds meaning it should be able to fire twice as long without reloading).