shock troops
From Longman Dictionary of Contemporary Englishshock troopsˈshock troops noun [plural] soldiers who are specially trained to make sudden quick attacksExamples from the Corpusshock troops• Against fast moving shock troops such as armoured cavalry this is also true.• The shock troops are: Eric, a chartered surveyor with a Doctor Who-length scarf.• The wars of this period presented little opportunity to shock troops fighting on horseback.• Its guitar-twanging shock troops led the charge away from what Ulan Bator had been, and toward what it was becoming.