I'm interested to work in the Narcotics Task Force for the Dallas Police Department?

I know that I must start off as a regular police officer,but what do I have to do afterwards?..If there is no opening for the Narcotics Unit,then I want to work in another task force that focuses on dealing with crime. I would rather work in specialized crime units rather than being a typical patrol officer,but I have no intentions to work as an undercover.