Complex sentence: He is surrounded and about to be executed when a machine he's purchased, a virtual cathode oscillator, destroys the machinery in Manning's home and disables all the "smart guns" that are trained on him.
Split into simpler sentences: He is surrounded and about to be executed when a machine he's purchased goes off. The device, known as a virtual cathode oscillator, destroys all the machinery in Manning's home, and disables all the "smart guns" that are trained on him.