The Operations Section Chief is responsible for establishing tactics for the assigned operational period. The Incident Commander (IC) and any Planning Chief will determine the overall objectives and priorities and will coordinate the Incident Action Plan with the Operations Chief, among others.
ADDED: In terms of law enforcement activity - the ranking on-scene commander.
According to ICS (Incident Command System), that responsibility falls on the Incident Commander (IC). As the size of an incident increases, those tasks are divided amount individuals within special sections.
Once an incident is large enough, the "Planning Section" takes care of strategies and tactics. The "Logistics Section" handles the ordering and release of resources.
All of this is coordinated with the Incident Commander and Section Chiefs.
Incident Commander
Incident Commander
The Incident Commander
Command
Incident Commander
Incident Commander
Incident Commander
Incident Commander
incident commander
Incedent commander
Incident Commander
Incident Commander
Incident Commander