Washington(CNN) Russia has been thwarting US-made mobile rocket systems in Ukraine more frequently in recent months, using electronic jammers to throw off its GPS guided targeting system to cause rockets to miss their targets, multiple people briefed on the matter told CNN.
Ukrainian military officials, with the US’ help, have had to come up with a variety of different workarounds as it continues to use the High Mobility Artillery Rocket System (HIMARS) which has been perhaps the most revered and feared piece of weaponry in Ukraine’s fight.
The medium-range rocket systems were hailed as a game changer in the conflict and have played a key role since the moment they arrived in Ukraine last summer, including in last year’s offensive that allowed Ukraine to take back significant swaths of territory from Russia.
But in recent months, the systems have been rendered increasingly less effective by the Russians’ intensive blocking, five US, British and Ukrainian sources tell CNN, forcing US and Ukrainian officials to find ways to tweak the HIMARS’ software to counter the evolving Russian jamming efforts.
“It is a constant cat-and-mouse game” of finding a countermeasure to the jamming, a Pentagon official said, only to then have the Russians counteract that countermeasure. And it is not clear how sustainable that game is in the long term.
With a major Ukrainian counteroffensive expected to start very soon and Ukraine’s reliance on HIMARS, solutions are even more of a priority so that Ukrainian troops can make significant headway.
“It’s one thing to be able to hold the Russians off where they are right now. It’s another thing to drive them out,” retired US Army Brig. Gen. Steven Anderson told CNN. “They’re dug in, they’ve been there for a year.”
Ukraine needs to keep ‘HIMARS in the game’
HIMARS “have been extremely important,” he added. “They have to be able to keep those HIMARS in the game and keep using them to be able to make effective deep strikes.”
Ukraine has received 18 American HIMARS to date and the US has committed to sending 20 more. Other NATO allies have donated 10 Multiple Launch Rocket Systems, according to the State Department.
The routine announcements from the Biden administration of hundreds of millions of dollars of military aid for Ukraine, including one on Wednesday, regularly include HIMARS munitions, called GMLRs, as a top item, though notably the exact number is not revealed.
The US has also helped the Ukrainians locate the Russian jammers and destroy them — a “high priority” effort, according to a secret Pentagon document that was part of a trove allegedly leaked by Airman Jack Teixeira.
“We will continue to advocate/recommend that those jammers are disrupted/destroyed,” the document says, “to the maximum extent possible.”
GPS jamming can affect other “smart” US munitions like the precision-guided Excalibur artillery shells fired from Howitzers and air-dropped bombs called JDAMs. The leaked Pentagon document described the JDAMS as being particularly susceptible to the disruption.
A US official confirmed that the US has been advising the Ukrainians on how to identify and destroy Russian jammers since there are a limited number of ways to modify HIMARS and their rockets.
Pentagon official downplays impact of jamming efforts
A senior Pentagon official downplayed the impact of the interference, telling CNN that on Monday Ukrainian forces fired 18 rockets without issue, about the daily rate of the past few weeks. The official declined to comment on the broader impact of the jamming. HIMARS are manufactured by Lockheed Martin, which deferred questions on jamming to the US government.
Electronic warfare is carried out by both sides, up and down the front line where there is heavy drone activity used for surveillance and in partnership with artillery targeting. The hardware can also be mounted on or around whatever might be targeted.
Depending on the location and strength of the jamming, a rocket can still launch and result in a successful strike with significant damage. In addition to GPS guidance, the rockets have inertial navigation systems that are not susceptible and remain accurate, though not as precise as when guided by GPS coordinates.
Widespread Russian jamming can have drawbacks for their own forces as well, impacting their ability to communicate and operate.
But even when they do function, the HIMARS have increasingly been missing targets, said one Ukrainian source briefed by drone operators on the frontlines.
One drone pilot on the Eastern front described the jamming of the mobile HIMARS as “significant,” according to the source, something he hadn’t seen in his area before last November, several months after the HIMARS first arrived in Ukraine at the beginning of the summer.
Another drone operator in the southern Kherson region claimed to the source that the effectiveness of HIMARS was down dramatically while cautioning that they’re still very necessary and relied on but no longer as dominant as they once were.
For nearly a year, the HIMARS system has been the longest-range rocket system Ukraine has, allowing troops to fire up to six rockets in quick succession at Russian positions as far as 50 miles away. With an accuracy of around 10 feet, the 200-pound warheads have taken out logistics hubs, ammunition depots, command posts and communication nodes, among other targets.
They were also instrumental in helping Ukraine retake significant amounts of territory in the south and northeast last fall, and as of February, Ukraine had expended approximately 9,500 HIMARS rockets, according to a daily update from the time reviewed by CNN.
A US official familiar with the workarounds said they include updates to the software on both the targeting system software as well the rockets.
The senior Pentagon official described it as: “constant tweaking to get them to stay effective,” adding that updates had been made as recently as this week.
“If their jamming gets more sophisticated, then your countermeasures have to get more sophisticated,” a British official agreed.
Russia’s use of electronic warfare has not been nearly as widespread as expected when Russia first invaded but they have made use of it since the beginning of the war. It’s a routine part of modern warfare that can be cheap and easy to implement. It’s expected, so the focus is on ways to “dilute” the impact, the official said.
But with Russian units largely stalled on the Ukrainian frontlines and stuck in defensive positions, Russian forces have made increasing use of their jamming systems to counteract the HIMARS, sources said.
A separate but related problem for Ukraine is that the Russians have been moving some of their equipment further back and out of reach of the HIMARS systems, which have a range of about 50 miles.
While the rocket systems are capable of firing longer-range missiles called ATACMS — which can reach targets over 185 miles away — the US has resisted providing them to Ukraine both because the missiles are in limited supply and because the US is worried Russia would see them as too provocative.
The British official acknowledged that since HIMARS were first introduced, the requirements, the training and supplementary equipment has changed as Russia’s electronic interference has evolved.
“Jamming is like the weather or the terrain, it’s something that happens that you have to deal with,” the official said. Still, he added, HIMARS remains a “highly useful piece of kit.”
CNN’s Oren Liebermann contributed reporting.