The High Mobility Artillery Rocket System, or Himars, involves trucks that can carry satellite-guided rockets and strike targets up to about 185 miles away with high precision. SYDNEY—Australia said it will acquire a highly mobile, U.S.-built rocket system that can strike targets from far behind the front lines, the latest step by the U.S. ally to beef up its military amid increased competition with China in the region. The system, the High Mobility Artillery Rocket System, or Himars, has gained prominence after being used effectively by Ukrainian forces against Russia. The system involves trucks that can carry satellite-guided rockets and...