Ukraine's use of drones to counter Russia's invasion is changing the nature of war. The United States has sent 600 more AeroVironment Switchblade drones to help the Ukrainian military counter Russia's invasion, the US Defense Department revealed Thursday. That's a major increase from the 100 drones the US sent in March. The drones are "loitering munitions" that can circle above a battlefield before in effect becoming missiles that attack specific targets. They're included in the Pentagon's new $800 million in military aid to Ukraine, a package that brings the country's total contributions to $2.6 billion in security assistance. The US...