Ship Conversion: USS Zumwalt Modified for Hypersonic Missiles

• What has been described as the most transformational warship in the U.S. Navy has been transformed again. USS Zumwalt (DDG 1000) recently completed modifications to remove her main guns and replace them with a hypersonic missile capability.  The work to have her guns removed to make space for new weapons was conducted at Ingalls Shipbuilding in Pascagoula, Miss.  

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With the modifications, Zumwalt  now carries four “all-up round canisters” for the Conventional Prompt Strike (CPS) missile in place of the forward Advanced Gun System (AGS) gun mount.  Each canister can carry three hypersonic CPS missiles.  The Army and Navy are jointly testing the new missile, which flies at five times the speed of sound and can strike targets 1,725 miles away.

The CPS missile has long been planned for launched from submarines. In 2023 the Navy contracted with Lockheed Martin adapt the system for use on the DDG 1000 class of surface combatants.

The Zumwalt class is the U.S. Navy’s largest surface combatant, and was originally armed with two AGS mountsa.

“We'll still have some work to do on 1000 in the water, but she will have been on land about a year, where all the big structural work was done,” said Kari Wilkinson, executive vice president of HII and president of Ingalls Shipbuilding. She was recently promoted to serve as president of the company’s Newport News Shipbuilding (NNS) division, effective Jan. 1, 2025.  
Image courtesy HII

The 600-ft., 14,564-ton Zumwalt arrived at the yard in August of 2023 and was taken out of the water and moved to a land-level area to conduct the structural work.  Upon completion, she was moved onto a drydock and then floated on Dec. 6, 2024.

According to Kiana A. Raines, a public affairs officer with Naval Sea Systems Command (NAVSEA), both mounts were removed.  “The area previously occupied by Mount 61 — [the forward 155mm or 6-inch gun mount] — will be repurposed for CPS.  The space previously taken up by Mount 62 “will remain open for future capabilities.”

The third ship in the class, USS Lyndon Johnson (DDG 1002), already had arrived at Pascagoula in January of 2022, to undergo her combat system activation.  DDG 1000 came around from her homeport of San Diego to undergo her replacement of AGS and other repairs.  

“We'll still have some work to do on 1000 in the water, but she will have been on land about a year, where all the big structural work was done,” said Kari Wilkinson, executive vice president of HII and president of Ingalls Shipbuilding. She was recently promoted to serve as president of the company’s Newport News Shipbuilding (NNS) division, effective Jan. 1, 2025.  

Because Lyndon John is already at the yard, she will also have her AGS system removed. “It will be more efficient with 1002 because they’re already here,” said Wilkinson.

USS Michael Monsoor (DDG 1001), remains on the West Coast, but will eventually come to Ingalls to have her weapons system updated.

“It made sense for the Navy to choose a build yard to do this work, because of the nature of the work, the amount of structure involved, and having to put the ship on land,” Wilkinson said.

DDG 1000 arrives for removal of AGS and installation of CPS.
Image courtesy HII

Typically, the Pascagoula yard’s work involves new construction instead of repair or modernization.  But there are some notable exceptions, such as the rebuilding of USS Cole (DDG 67) after she was severely damaged in a 2001 terrorist attack; repairs to USS Fitgerald (DDG 62), which collided with a merchant ship in the South China Sea in 2019; as well as the modifications to the Zumwalt class.

Ingalls is one of two yards that are building the Arleigh Burke (DDG 51) class of AEGIS guided missile destroyers (DDGs) (along with General Dynamics Bath Iron Works (BIW) in Maine), and is the only yard building amphibious ships for the Navy—currently the amphibious transport dock (LHD) and Flight II San Antonio-class LPDs; as well as the Coast Guard national security cutters. It is also the largest manufacturing employer in the state.  

BIW, the construction yard for the Zumwalt class, was an “excellent partner,” Wilkinson said.  “They shared a lot of information with us to make sure that we were all successful.”

• Evolving Weapons Capabilities

The AGS gun and LRLAP ammunition were derived from the Army’s 155mm long range Excalibur howitzer program.  In fact, in 2016 the Navy considered using the existing Army ammunition instead of creating the more capable but more costly ammunition.

Although the Navy shelved its electromagnetic rail gun several years ago, that technology was also considered for the Zumwalts, in part because the ship has the power resources required.

The AGS gun was cancelled not because it didn’t work, but because the bullets became unaffordable, and Navy priorities shifted from the littorals to blue water peer competitors — China and Russia — than asymmetric threats in the littorals.  Moreover, the Marines are focused on distributed maritime operations, with less emphasis on large scale amphibious landings requiring fire support.

A report from the Congressional Research Service stated, “In December 2017, it was reported that, due to shifts in the international security environment and resulting shifts in Navy mission needs, the mission orientation of the DDG-1000s would be shifted from an emphasis on NSFS (naval surface fires support) to an emphasis on surface strike, meaning the use of missiles to attack surface ships and perhaps also land targets.”

Nevertheless, AGS was a marvel of engineering, with incredible accuracy and range of the rocket-assisted LRLAP projectiles.  DDG 1000 was designed to be stealthy, particularly useful in littoral operations, although the current focus is on a possible open ocean confrontation.  The plans for the class were cut from 32 to 24 to 17 to 7, then two…and eventually three—in fact, at one point, the entire program was threatened with cancellation.  But with the class reduced to just three ships, the cost of the ammunition was just too costly.

U.S. Navy Strategic Systems Programs and the Army Hypersonic Program Office successfully conducted a High Operational Tempo for Hypersonics flight campaign. This test informed the development of the Navy’s Conventional Prompt Strike and the Army’s Long Range Hypersonic Weapon offensive hypersonic strike capability. (U.S. Navy Photo/Released)

• New Technologies

The Zumwalts incorporated a plethora of transformational technologies.  They included a wave-piercing, tumblehome hull; a composite helicopter hangar and deckhouse (the third ship in the class has conventional steel topside structures); a total-ship computing environment for the IT backbone for communications and systems management; an integrated electric-drive propulsion system with advanced induction motors; a peripheral vertical launching system; and the now-cancelled advanced gun system (AGS); and more.

The investment in DDG-1000’s stealth was substantial.  It was very difficult to detect on radar, and quiet so as to be hard to locate by sonar. DDG 1000 had significant ASW capabilities in the littoral.

The Zumwalts still have 80 peripheral vertical launch system cells along the sides of the ship, able to hold a variety of missiles, to include Anti-submarine Rockets (ASROCs) and quad-packs of NATO Evolved Sea Sparrow Missiles; as well as two 33 mm guns.