4. The Predator and Predator B (aka The Reaper)
The Predator B or Reaper is the successor to the MQ-1 Predator, which has seen action in Iraq, Afghanistan, Bonsia, Serbia, Pakistan and Yemen.
The Predator is so significant and terrifying because it is the first unmanned aircraft ever to engage in armed combat.
A Predator was shot down by an Iraqi Mig-25 after firing a missile at it in 2002.