hmm, so your plan was sneak in, place the singing rock that can make a distraction to the enemy, and destroy there admiral (well that a suicide mission)
second, maybe the singing rock was a jammer
@Foxhound87 That rock was mentioned a few chapters back (ch7), it is a beacon for some sort of alien fleet. A fitting tool to slow down and weed out enemy forces. Not that much of a suicide mission. Would raise some question though... Kinda risky to use it in front of public eye.
@HiraOmnibus spoilers should be in spoiler tags, even if they're small spoilers.
That said, this is one manga where I do recommend reading the light novel. The manga has been fairly faithful so far, and the novel is a good read, and several volumes ahead (manga still in vol.1, novel is ~vol.4).