Though the invaders' spaceship in the scenes toward the film's end is supposed to be invisible, it's actually visible throughout the sequence until just before it's destroyed, when it briefly does become invisible.
It's repeatedly stated that the invaders' major advantage against the Earth is the fact that they're invisible. Yet by inhabiting the bodies of dead Earthmen, they give up this advantage, to no obvious purpose.
The B-17 bomber crashes into a target laid out in sandbags on the ground. It is stock footage of an Air Force test experiment related to remote-controlled flying bombs. In practice, the plane would have been pilotless and would have been loaded with high explosives.