US President Joe Biden on Friday authorized fresh $275 million in military aid for Ukraine offering new capabilities to defeat drones and strengthen air defenses, according to a memo released by the White House.  The package also includes rockets for High Mobility Artillery Rocket System (HIMARS) launchers made by Lockheed Martin Corp, 80,000 155mm artillery rounds, Humvee military vehicles and about 150 generators, according to the memo.  This is the 27th use of Presidential Drawdown Authority (PDA) for Ukraine, which allows the United States to transfer defense articles and services from stocks quickly without congressional approval in response to an emergency.  National Security Council spokesman John Kirby told reporters at the White House that the equipment was "on its way."  But details were scant on two systems, "counter air defense capability" and "Counter-Unmanned Aerial Systems equipment," which appear to be new capabilities for Ukraine.  Russia's surge in missile strikes in Ukraine is partly designed to exhaust Kyiv's supplies of air defenses and achieve dominance of the skies above the country, a senior Pentagon official said in November.  To counter these attacks, the United States has sent sophisticated anti-aircraft NASAMS systems to Ukraine which have been running for a few weeks.  Washington previously announced that it was sending four Avenger short-range air defense systems that use Stinger missiles, made by Raytheon Technologies Corp, and HAWK interceptor missiles.  US allies have also been sending air defense systems.  Since the Russian invasion of Ukraine on Feb. 24, which Moscow calls a "special military operation", the United States has sent about $19.3 billion worth of security assistance to Kyiv.