The U.S. Army's Special Forces, better known as Green Berets, have had a deep impact on Ukraine's fight to defend itself from a Russian invasion, despite not being directly involved in the conflict.

"Ukraine was taken very seriously by Special Forces," retired Green Beret Sgt. Maj. Martin Moore told Fox News Digital. 

After Russia's annexation of Crimea in 2014, a move that faced minimal resistance, the Ukrainian military began an effort to modernize its forces to prepare for possible further Russian incursions into the country. The U.S. military also quickly stepped in to help, with the Army's Green Berets taking on a critical role in training Ukrainian forces.

Russia invasion Ukraine soldier

Ukrainian soldiers take positions outside a military facility (AP Photo/Emilio Morenatti)

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"They immediately set upon a great effort to protect to Ukraine, to provide training," Moore said. "There's nobody better at training than Green Berets. These are people that can teach."

While elite military units such as the Navy SEAL teams garner widespread attention, the Army's Green Berets are fanned out across the world helping armies prepare for wars similar to the one now being fought in Ukraine. This work is typically done quietly, something Moore said Green Berets prefer.

"They do something different," Moore said. "They go where nobody else is and find out what is possible."

Moore said Green Berets are a "force multiplier," improving the combat capability of the international forces they work with. He stressed that they are not about "raids and ambushes," but about having an "unparalleled understanding of the place" where they are operating. 

A Green Berets U.S. Army Special Forces Group soldier in action

A Green Berets U.S. Army Special Forces Group soldier in action

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Green Berets are required to learn a foreign language as part of their training and are constantly trained in the political, economic and cultural complexities of the regions in which they are assigned to operate. This unique skill set allows them to partner with foreign forces for training and at times to fight alongside them.

Those skills have been put to use in Ukraine since 2014, with Green Berets and members of the Army's National Guard advising and training Ukrainian forces at Yavoriv Combat Training Center in western Ukraine. It's the same facility Russia attacked with rockets on March 13, killing 35. The Americans had already left,  vacating the facility and moving troops deployed there to Germany in February. 

Part of the job Green Berets did at Yavoriv was to train their Ukrainian counterparts to set up militia units that could wage guerrilla warfare against an invading force. The Ukrainian military can now put those lessons to use, with the government actively encouraging its citizens to join the fight against Russian forces.

Civilians practice moving in groups at a military training exercise conducted by the Prosvita society in Ivano-Frankivsk, Ukraine, on Friday, March 11, 2022. (Alexey Furman/Bloomberg via Getty Images)

Civilians practice moving in groups at a military training exercise. (Alexey Furman/Bloomberg via Getty Images)

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But the work Green Berets are doing in Europe hasn't stopped, with forces still stationed in Europe helping prepare partner countries for the possibility of a Russian invasion farther into Europe. Such a move would be a mistake for Russia, Moore told Fox News Digital, arguing that the invasion of Ukraine has already gone poorly in part because of U.S. assistance, and a further move into NATO territory would go even worse.

"Russia has a horrible thing waiting for them if they want to push this thing further," Moore said.