Mk45 Mod4, a 5″ gun 62 calibers in length
The US Naval Institute reports that during an unclassified exercise as part of RIMPAC USS Dewey (DDG-105) fired 20 hyper velocity projectiles (HVP). The rounds were fired from a 5″/62 Mk45 Mod4.
Back in 2012, I published a post “Case for the Five Inch Gun.” My conclusion was
In choosing the Mk110 57mm because it was seen as a better AAW weapon, a better anti-swarm weapon, as lighter, cheaper, easier to maintain or man, for whatever reason, the Coast Guard will have a weapon that is at best only marginally more capable, perhaps even less capable, of performing the most likely missions–stopping/sinking a surface target or performing NSFS–than the weapons of 60 to 90 years ago.
While the size, toughness, and survivability of merchant ships has increased dramatically, the Coast Guard has not provided its ships with a significantly improved capability to stop or sink a ship since the introduction of the 5″/51 in 1921. I still think the Coast Guard should add a light weight anti-surface vessel torpedo to its inventory as the cheapest way to have a truly effective ship stopper that can be made widely available. But until such a weapon becomes available, the Mk45 5″ is the best alternative available.
The 5″ Mk45 is a versatile weapon. Equipping the OPCs with this weapon make the ships more capable of performing both the PWCS and probable wartime mission and significantly enhances the NSFS capability of US Naval forces in a major conflict.
I think the argument for the 5″ just got a lot stronger. The test involved shooting guided rounds at a target of cruise missile size and speed. That has got to mean extreme accuracy against even moving targets.
Adding this capability to Cutters would increase both their survivability and their offensive capability. In addition it would substantially increase their capability to forcibly stop a vessel of almost any size since the projectiles, about seven times heavier than an 57mm round, would be traveling at near hypersonic speeds, they would likely disable any engine it hits by kinetic energy alone.
An artist’s conception of BAE Systems’ Hyper Velocity Projectile. BAE Systems Image
I have not seen any particular kind of guidance identified for this test. The illustration above does appear to show a panel, presumably one of four, between the fins at the base of the projectile.
“So if you think about the kinds of threats you might face in the Middle East, the lower-end cruise missiles or a larger UAV, now you have a way to shoot them down that doesn’t require you use a $2 million ESSM or $1 million RAM because a hyper velocity projectile – even in the highest-end estimates have it in the $75,000 to $100,000 range, and that’s for the fanciest version of it with an onboard seeker,” he said.
An added benefit of using HVP in powder guns is the gun’s high rate of fire and a large magazine capacity.
The projectiles apparently weigh about 45 pounds, and may cost as little as $25,000, far less than even the relatively cheap RAM short range anti-air missile at about $1M each. Range is expected to be about 40 miles when fired from a 5″ gun.
The Mk45 Mod4 was first installed on the USS Winston Churchill (DDG-81) commissioned in 2001, superseding the earlier 5″/54 Mk45 mods. Since then it has been the standard USN 5″ gun. It is also in service with the Australian, South Korean, Japanese, and Danish Navies, and they will arm the British Type 26 frigate. Earlier models of the 5″ Mk45 also serve in the Navies of New Zealand, Greece, Spain, Turkey and Thailand.
The gun mount is not a lot larger than the 5″/38 Mk30 mounts that were used on over 50 Coast Guard cutters (255s, 311s, 327s, 378s, and icebreakers) between the early 1940s and their removal from the 378s in the late ’80s and early 90s. In fact the early models of the Mk45 were designed as a drop in replacement for the 5″/38.
Earlier 5″/38 mounts used by the Coast Guard were highly manpower intensive requiring 14 to 15 to fully man the mount and pass projectiles and powder. Full manning for a Mk45 Mod4 is only six, a Gun Captain, Panel Operator and four ammunition Ioperators, all below deck. It can fire up to twenty rounds before the four ammunition operators arrive on station, allowing relatively easy Condition III manning.
The 5″/38 mount weighed about 41,000 pounds. The Mk45 Mod4 is estimated to weigh 50,456 lbs. (22,886 kg) without a lower hoist and 54,398 lbs. (24,674 kg) with a four-flight lower hoist. that is at most a 33% increase.
Time to Think about an OPC “B class”
What the Soviets used to call the correlation of forces is changing. The Navy’s top surface warfare officer told a gathering at the Surface Navy Association Seminar, For the ship crews, “we need to have them prepared on a moment’s notice to turn the readiness we are building into lethality,” that they had to be ready to fight now.
It is time for the Coast Guard to start reasserting its military nature. Hopefully we have at least a few years to rebuild the Coast Guard’s capability as a naval force which was discarded after the Soviet Union fell apart
It is not too early to start thinking about a “B class” OPC. Replace the 57mm with the 5″/62 Mk45 mod4, replace the 25mm Mk38 with SeaRAM. Add the sensors from the LCS ASW mission module at the stern. Add some Anti-Ship Cruise Missiles Forward. Make sure we have space to support MH-60R ASW helos it is supposed to be able to hangar with torpedoes and sonobuoys. That is not a whole lot different from the systems we had on the FRAM 378s, and the OPC is a third again as large.
USCGC Mellon seen here launching a Harpoon anti-ship cruise missile in 1990.