Former Rep. Chris Stewart, a former fighter pilot, says the U.S. isn’t prepared for this change in modern warfare.

Russia launched large-scale drone and missile strikes on Ukraine's capital and other parts of the country early on Friday, local officials said. At least four people were killed in Kyiv and at least 20 have been injured, the city's mayor Vitaliy Klitschko said.

Drones are “ubiquitous, because they are quite useful, and they're demonstrating that every day in Ukraine,” one analyst told NBC News.