reaction, noun
Used attributively in the phrases reaction police, reaction squad, reaction unit, designating a police unit which specializes in the control of crowds and rioters, and which is on standby so that it can react quickly when summoned.
1982 E. Prov. Herald 2 Sept. 1The reporter saw the morning convoy as it sped along Settlers Way,..three reaction unit vans, three large police transporters and two buses.
1987 Argus 8 July 3The former commander of the Bellville reaction unit..has been relieved of his riot duties.

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