Ukraine has been using British-built versions of the digital jammer—about the size of a computer tablet—on long-range strike drones already this year. But the agreement allows the country to mass-produce it themselves so it can be more rapidly scaled across their drone forces.

The British government announced the existence of Stone Cloak for the first time on Saturday as Ukrainian President Volodymyr Zelenskyy met with the new prime minister at a naval base in Portsmouth. The occasion is the annual Sea Breeze joint exercise. Ukrainian, U.S. and British sailors paid “special attention” to countering Russian air defenses during this year’s Sea Breeze according to Ukraine’s national news agency.

“At this point, we don't know the full details of Stone Cloak, but suffice it to say, the system will likely increase mission effectiveness against some of the Russian air defenses,” Jeffrey Fischer, a retired U.S. Air Force officer, told Defense One via email. 

Ukraine uses a variety of electronic warfare systems as part of its drone operations. But the ones provided by partners like the U.K. are often backed by larger research budgets. Operators and developers can also test them in a more controlled environment than the Ukrainian battlefield. But they can emulate the unique electronic warfare aspects of such places–so long as Ukrainian operators are allowed to participate, such as the Hedgehog 2025 exercise in Estonia in which the participating Ukrainian team exposed large gaps in NATO drone warfare concepts. That’s why new technology emerging from joint Ukrainian-allied exercises is a big deal. But the actual sharing of intellectual property related to that technology is more rare.

British Prime Minister Andy Burnham on Monday described Stone Cloak as “the best of homegrown British innovation, and proven on the frontline” of Russia’s war on Ukraine. That frontline has moved back toward Moscow, thanks in small part to British-donated Storm Shadow missiles, which Ukraine has been using to hit targets in occupied territory going back to 2023. However, the United Kingdom never transferred the actual design technology to Ukraine, just the missiles themselves.

The new announcement shows how quickly technology sharing between the two countries has evolved in just three years, as well as the speed of Ukrainian weapons development and manufacturing compared to some NATO counterparts. 

The United Kingdom spent six years developing and deploying Storm Shadow. Manufacturing relied on specialized European supply chains. French and Italian partners were involved, which made a tech transfer bureaucratically difficult. And the missiles were expensive gifts, averaging $2 million apiece.

These and other factors compelled the U.K. and Ukraine to enter into a joint agreement to develop a new long-range strike drone with streamlined and simplified requirements—a 2024 effort called Breakstop that British officials say will deliver missiles for frontline use later this year. That timeline—less than 24 months from concept to full deployment—is far faster than Storm Shadow and much less expensive. Meanwhile, Ukraine also announced its own long-range strike missile, the Flamingo, or FP-5, which is also capable of striking Russia but costs much less than the Storm Shadow.

 Fischer said that the contrast in innovation speeds helps explain how such intellectual-sharing partnerships help the United Kingdom as much as they do Ukraine. “One critical but often overlooked lesson from the Ukraine war is the extremely rapid adaptation cycle Ukraine is able to implement. In some cases, battlefield lessons are implemented in less than 10 days to new systems. In my seven combat deployments, NOTHING has ever come close to that.”