The rank of police corporal is correlational to the rank of corporal

Corporal

Corporal is a rank in use in some form by most militaries and by some police forces or other uniformed organizations. It is usually equivalent to NATO Rank Code OR-4....

 in the armed forces

United States armed forces

The United States Armed Forces are the military forces of the United States. They consist of the Army, Navy, Marine Corps, Air Force, and Coast Guard.The United States has a strong tradition of civilian control of the military...

, typically ranking immediately above officer

Police officer

A police officer is a warranted employee of a police force...

 and immediately below sergeant.The position is also referred to by some agencies as Agent.

Function

A police corporal is generally employed as an officer with additional leadership responsibilities. These duties may include one or more of the following roles:

• Detective
  Detective
  A detective is an investigator, either a member of a police agency or a private person. The latter may be known as private investigators or "private eyes"...
  
  
• Field Supervisor
• Field Training Officer (FTO)
  Field Training Officer
  A Field Training Officer is an experienced or senior member of an organization who is responsible for the training and evaluation of a junior or probationary level member...
  
  
• Watch Commander, and others

Police corporals will often act as a lead officer in field situations when a sergeant is not present.

Occurrence

The rank is not present in all police agencies and is generally dependent upon the size, funding, command structure, as well as the traditions and history of an individual agency.