The enormous expansion of drone warfare is forcing militaries to reconsider how much ammunition they can afford to fire at relatively cheap targets. The Pentagon is betting that some of that ammunition can be replaced with electricity, selecting four directed-energy systems for operational testing at five U.S. military bases. The Pentagon selected AeroVironment’s (NASDAQ: AVAV) Palletized High-Energy Laser, Boeing’s (NYSE: BA) Compact Laser Weapon System, Kord Technologies’ Firefly high-energy laser and Epirus’ Leonidas…