US spies have provided Ukraine with detailed intelligence about Russia's moves helping slaughter eight generals, 36 colonels and 300 officers.
It has dealt a huge blow to Vladimir Putin who lost his 35th colonel in Moscow last week during the Ukraine war.
Col Mikhail Nagamov, 41, from the sixth engineer-sapper regiment from the Yaroslavl region, died on April 13 "while performing a combat mission" in Ukraine.
American officials said the US helped Ukraine target Russian forces by sharing intelligence on when missiles and bombs were intended to strike.
"From the get-go, we leaned pretty heavily forward in sharing both strategic and actionable intelligence with Ukraine.
"It’s been impactful both at a tactical and strategic level. There are examples where you could tell a pretty clear story that this made a major difference," one official told NBC News.
The agreement was part of a huge, unprecedented intelligence sharing operation with a non-NATO partner.
US officials say it has played a crucial role in Ukraine's success so far against a larger and better-equipped Russian military.
More than 20,000 troops have already lost their lives to Putin's invasion, according to estimates.
Major General Vladimir Frolov, deputy commander of the 8th Combined Arms Army, became the latest general to be laid to rest earlier in another major blow to his war effort.
“There has been a lot of real-time intelligence shared in terms of things that could be used for specific targeting of Russian forces,” an ex senior intelligence official told NBC.
This includes commercial satellite images and other intelligence such as where certain types of Russian units are active, they added.
The publication has agreed to hold back some details about the operation at the request of the US military amid concerns it could help Russia close down important sources of information.
Officials said fighters in Ukraine were able to hit a Russian transport plane near Kyiv thanks to coordinates supplied by the US.
The strike proved crucial in the battle for the capital as it weakened Putin's troops who were forced to use the road instead of the airfield.
Another official told of certain instances where Ukraine was able to move aircraft and air defences just in time.
"The Russian military has literally been cratering empty fields where air defences were once set up," they said adding that this has had an "enormous" effect on Russia's ground troops.
While another claimed that the CIA aims to help protect Ukraine's president Volodymyr Zelensky and is in communication with the country on "how best to move him around."
The intelligence gathering mission also aims to consult with Ukraine in order to make sure Zelensky is "not co-located with his entire chain of command, things like that", the source added.
