Chain of Command

What exactly is 'Chain of Command'?

Chain of Command is in essence, who is in charge. In Certain situations (In absence of a Captain) some Heads of staff are at the lead of the Chain of Command.

The list goes as followed:

Interim Heads of Staff

In the event that a department is lacking a Head of Staff, someone with enough training can be assigned as a Interim Head of Staff by another command member.