The U.S. has played a quiet but crucial role as Ukrainian troops have made stunning gains this week in a counteroffensive that dealt an embarrassing blow to Russian forces. 

Kyiv’s military strategy, which has allowed it to take back thousands of kilometers worth of Russian-occupied territory within days, is the cumulation of months’ worth of planning helped by U.S. war modeling and expertise.  

In addition, artillery and heavy weapons provided by the U.S. have provided immediate firepower and long-term confidence that Ukraine’s troops will remain equipped for the longer fight. 

“What you’re seeing now is real unity in action,” a senior defense official told The Hill, adding that Ukraine’s current successes are the result of “incredible resolve from our allies, partners, and from the Ukrainian people, really, at every level.” 

As of Thursday, Ukrainian troops had taken back nearly all of the Kharkiv province in the northeast and continued to liberate several villages in the southern Kherson region, according to officials in the country. 

The gains are part of a two-front counteroffensive that began at the start of September and made major headway in the past week — particularly in Kharkiv, where Ukrainian troops’ lightning-fast advance seemed to catch Russians forces on the back foot and forced them to rapidly retreat. 

President Volodymyr Zelensky said earlier this week that Ukrainian forces had retaken 6,000 square kilometers (2317 square miles) of Russian-held territory since the beginning of the month — about 3,400 kilometers (2113 miles) of that in the north just in the last week.   

The rapid territory gains — more than the Russians have made in the past five months — even took Ukrainian and Western officials by surprise. 

But the counteroffensive was the result of months of discussions, war strategizing and intelligence sharing between senior U.S. and Ukrainian officials, as well as a steady buildup of Ukrainian firepower with the help of U.S. weapons shipments, according to defense officials and experts.  

Zelensky in midsummer relayed to his top military brass that he wanted to make a major push to show that Ukraine could kick back at the Russian incursion, and had his generals create a plan for a broad offensive across the south and east, CNN first reported. 

The strategy, which was then shared with U.S. defense officials, was assessed to likely fail, and the Ukrainians went back to the drawing board, according to The New York Times. 

The senior defense official confirmed that “over the summer,” the Pentagon “provided advice during the war games, and then the Ukrainians internalized that and made their own decisions.” 

Through “regular dialogue” with their Ukrainian counterparts, U.S. officials were able to “understand evolving requirements” and “synchronize with allies, partners, and Ukraine around the clock” to provide needed weapons and intelligence to help the Ukrainian forces, the official said.    

And top Pentagon spokesperson Brig. Gen. Pat Ryder on Tuesday acknowledged that Washington has been sharing “time sensitive information” with Kyiv, but declined to provide specifics.  

The strategy ultimately deployed by Kyiv proved to amplify existing problems on the Russian side, including supply line and logistics issues, as well as a battered command and control that has hampered Russian troops in the six months since the war began.  

In droves, Russian forces fled from their positions, leaving behind ammunition stockpiles and equipment and, in some cases, falling back into their country across the northeastern border with Ukraine.  

“The biggest explanation you can give for why Ukraine is so successful is that they took the time, they were patient and they shaped the battlespace,” said Steven Horrell, a senior fellow at the Center for European Policy Analysis and a former U.S. naval intelligence officer. “They were very well prepared for this.” 

The carefully planned operations were then bolstered by U.S. weapons, including precision armaments such as the High Mobility Artillery Rocket System, which allows the Ukrainians to precisely strike and take out high-value Kremlin targets, Horrell said.  

As of this week, the U.S. has committed nearly $15 billion in lethal aid to Ukraine since the start of the Feb. 24 invasion, including a new $675 million package of weapons and equipment for Kyiv announced last week.  

And since April, the U.S. government has also led a 50-country effort known as the Ukraine Contact Group to coordinate the flow of military assistance to Kyiv.  

“Definitely the Western assistance of equipment, training on that equipment, but also intelligence sharing, contributed to the current Ukrainian successes,” Horrell said. 

Despite Ukraine’s recent successes — with country officials calling it one of the major turning points of the war — others have warned the fight is still far from over.  

United Nations Secretary-General António Guterres said Wednesday he thinks a peace deal to end the conflict isn’t likely anytime soon 

“We are far away from the end of the war,” he told reporters following a call Wednesday with Russian President Vladimir Putin, as reported by CNN. 

“A cease-fire is not in sight,” he added, “I would be lying if I said it would happen.” 

And Biden administration officials have been hesitant to label the quick Ukrainian territorial gains as a turning point in the war. 

U.S. defense officials point out that the Russians still have large amounts of manpower and weapons in Ukraine and still hold important territory, including key cities and towns in the easternmost Luhansk region.

Still unknown is whether Ukraine can keep the momentum and make headway into Luhansk, where Russian forces will try to hold the line.  

But Western governments say they are prepared for the long haul. 

“Russia’s efforts have not succeeded and will not succeed; and as we have made clear, we are committed to sustained assistance and support as Ukraine defends its sovereignty and territorial integrity,” the defense official said.