It is well known that America’s military dominates both the air and the sea. What’s less celebrated is that the US has also dominated the spectrum, a feat that is just as critical to the success of operations. Communications, navigation, battlefield logistics, precision munitions–all of these depend on complete and unfettered access to the spectrum, territory that must be vigilantly defended from enemy combatants. Having command of electromagnetic waves allows US forces to operate drones from a hemisphere away, guide cruise missiles inland from the sea, and alert patrols to danger on the road ahead. Just as important, blocking enemies from using the spectrum is critical to hindering their ability to cause mayhem, from detonating roadside bombs to organizing ambushes. As tablet computers and semiautonomous robots proliferate on battlefields in the years to come, spectrum dominance will only become more critical. Without clear and reliable access to the electromagnetic realm, many of America’s most effective weapons simply won’t work.