The Biden administration is preparing to announce a roughly $2.5 billion military aid package for Ukraine that is expected to include dozens of Bradley and Stryker armored vehicles, according to two people familiar with the decision, as the Pentagon intensifies its support ahead of an expected counteroffensive against entrenched Russian forces. The war has entered a phase, U.S. officials have said, that will require Ukrainian units to attack enemy forces in a concerted way, using tanks, armored vehicles, artillery and aviation in what is known as combined arms warfare. Bradleys and Strykers would significantly bolster their firepower and allow soldiers...