30mm “Swimmer” Round

30x173mm ammunition for Mk44 Bushmaster II

30x173mm ammunition for Mk44 Bushmaster II

Ran across an interesting new type of ammunition, the 30 mm Mk 258 mod 1 APFSDS-T, which appears to be designed specifically to counter Fast Inshore Attack Craft (FIAC). It uses a unique configuration to allow it to maintain high velocity after entering the water. Being an armor-piercing, fin stabilized, discarding sabot, tracer round, I suspect it might help us attack the engine rooms of larger ships. if we upgrade our Mk38 gun mounts to use the 30mm. Might be able to disable propellers and rudders as well.

In a test “…it destroyed a representative FIAC target travelling at 30kts at a range of 4.8km with the first shot.”

It would probably be good against radio controlled boats like the one in the recent attack off Yemen. General Dynamics is advertising that this “swimmer version” is currently available. This might explain why the Navy replaced the 57mm on the DDG-1000 class will 30mm guns. 

There is a bit more in the 2014 NAMMO Bulletin, on page 8 (5/13 on the pdf), under the title “The Navy’s Best Ammunition”;

The nose-shaped configuration was originally patented by the U.S. Navy and NSWC Dahlgren, but was never turned into functional ammunition. Nammo, NSWC Dahlgren and FFI (Norwegian Defense Research Establishment) carried out a comprehensive study that resulted in the final design configuration of the penetrator nose. Today, Nammo’s Mk258 mod 1 ammunition is used on board the LPD-17 and LCS class of U.S. Navy ships. This has significantly increased the fleet’s capability to defeat aerial and surface threats, as well as submerged threats like torpedoes and mines.

At the very least the 110s in Bahrain (or their Webber class replacements–whenever?) probably should have these. I’d like to see them on all the Webber Class WPCs.

2 thoughts on “30mm “Swimmer” Round

  1. This might be useful in disabling rudder and propeller too.

    On the other hand I don’t see a lot of advantage for AAW other than its high velocity (1430 M/sec or 4692 feet/sec.) which would give it a flat trajectory and shorter time of flight. If it were available, which it is not, a radar fuse on an explosive round, would be preferable, but really this is not an AAW weapon.

  2. Apparently there is a report comparing the accuracy of this round with conventional 30 mm rounds.
    NSWCDD/MP-07/21, “30-Millimeter ArmorPiercing
    Versus High Explosive Ammunition Comparison Test Report”
    Presumably it is classified, but it might be worth a look for those in a position to make decisions regarding weapons and ammunition.

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