SIMI VALLEY, CA -- The U.S. military service chiefs said today China and Russia's rise as great military powers pose significant and varied challenges to the Army, Navy, Air Force and Marines. During a panel discussion at the Reagan National Defense Forum here, the four service chiefs said Chinese and Russian activity in space, missiles and on the sea are driving thinking about how to reposition the U.S. military. Air Force Chief of Staff Gen. David Goldfein said China is...