These are automatic bonus attacks which deal heavy damage over a wide range, having the opportunity to make all your nearby enemies pay for the poor weapon choice of their officer. (glitchcat.com)
You can also combo your attacks, so like two light attacks followed by a heavy attack produce a certain bonus attack at the end. (blurayauthority.com)
The controls are the usual tower placement click and drag formula but there are some new additions in the form of bonus attacks or effects, such as calling in a lightning storm to damage enemy ships. (appspy.com)