Collisions, why won't they work?

I am making a game in which you may fire guided missiles. The missiles are added to the scene via an empty. They track to the enemy plane. I am trying to use the collision sensor to end the missiles when they hit the plane, take a life away from the plane, and add explosion objects. None of the collisions seem to be registering.

Is the missile dynamic?

Er, does it have to be?

At least “Actor”!