WashingtonCNN — Russia has been hindering US-created mobile rockets more frequently in Ukraine recently, using electronic jammers to overthrow its GPS-based targeting system, this causes rockets to misfire their targets, multiple people who were involved with the project told CNN.

Ukrainian military officials have had to invent multiple different solutions to the problem of their own equipment, with the American help, they have employed the High Mobility Artillery Rocket System (HIMARS) as the most celebrated and feared piece of military hardware in Ukraine's conflict.

The medium-range rocket systems were touted as a significant game changer in the conflict, and have had a significant role in the past year since their arrival in Ukraine last summer, including in the offensive that led to the takeover of territory that was significant to Ukraine last year.

However, recent months have seen the systems become increasingly less effective as a result of the Russians' increasing blocking, five American, British and Ukrainian sources tell CNN that the HIMARS have been modified to counter the Russians' increasing jammer device.

It's a constant pursuit of a solution to the cell phone jamming, a Pentagon official said, only for the Russians to then reverse the solution. And it's not clear how long-term the game is sustainable.

With a large-scale Ukrainian offensive expected to begin soon, and the country's reliance on HIMARS, solutions are now more important to make sure Ukrainian soldiers can gain significant advantage.

It's still one thing to successfully oppose the Russians at their current location. Another goal for them is to drive out the Americans, the retired US Army Brig. said. Gen. Steven Anderson explained to CNN. They're sunk in, they've been there for a year.

Ukraine needs to keep HIMARS in the game

HIMARS has been of great importance, he said. They must have the capacity to preserve these HIMARS and utilize them to perform effective punches.

Ukraine has currently received 18 American HIMARS, and the U.S. has pledged to send 20 more. Other members of NATO have given 10 Multiple Launch Rocket Systems to the State Department, according to the Department of State.

The common proclamations from the Biden administration regarding hundreds of millions of dollars in military aid for Ukraine, including one on Wednesday, typically include HIMARS weapons, called GMLRs, as the most significant item. However, the exact number is not revealed.

The U.S. has also assisted the Ukrainians in locating the Russian jammers and destroying them, a “important priority” task, according to a concealed document in the Pentagon that was part of a volume allegedly leaked by Airman Jack Teixeira.

The document continues by advocating for the continued destruction of jammers as much as possible.

GPS jamming can adversely affect other "intelligent'' US weapons like the guided Excalibur artillery shells that are fired from Howitzers and the air-dropped bombs called JDAMs. The document with the leaked Pentagon described the JDAMS as being particularly vulnerable to the disruption.

A U.S. official acknowledged that the U.S. has advised the Ukrainians on how to recognize and destroy the Russian jammers, because there is only a limited number of ways to alter HIMARS and their rockets.