Unity of command basically means that each police officer is only accountable to one superior officer at any one given time. Exceptions include assignments or line-of-duty emergencies.
Unity of command is basically the classical approach to police administration; it is by far the most popular approach due to its reduction in civil liability risks. The chain of command is strictly adhered to; any disciplinary action can be clearly accounted for and is in line with federal management command structures during homeland security crises.
When a police officer has to answer to a very specific superior officer, the superior officer is motivated to ensure that all his task members adhere to departmental and federal policies. His professional reputation and his career are at stake: allegations of abuse, bribery, misuse of deadly force, and/or discrimination against any group of citizens will have disastrous consequences, both for the supervisor and his department. Civil and/or criminal charges may be levied against him and his task force. This will jeopardize organizational stability, morale, and the chain of command structure.
So, how does unity of command work to promote responsible leadership and officer accountability?
1) No supervisor may order an officer to perform an illegal action.
2) A supervisory officer implements disciplinary actions on any subordinate at the direction of their own supervisory officer or the chief. The unity of command structure also allows unions representing officers to pinpoint any possible abuse or misconduct (within the chain of command) in requiring corrective action or termination. This system holds that any deficiencies in internal policy or training can be readily isolated with a certain level of ease, thus increasing efficiency and accountability within the police force.
3) Within internal affairs, supervisory officers account for any disciplinary action or couseling sessions with officers by filling out a Supervisor's report or counseling memo. Documentation is key to accountability, both for the supervisor and the subordinate. If counseling fails to reform the offending party, the supervisor can draft a Performance Improvement Plan that will be forwarded through the chain of command to the Chief of Police for final approval.
4) For issues between officers and the public, the unity of command structure ensures that supervisors are held accountable for the officers who serve under their leadership. For example, supervisors can be held liable for negligent retention if they allow an officer they know to be a risk to the public to stay on duty.
I hope this helps. Thanks for the question.