Line of Duty burst back into our lives [1] this month with the start of series six. To no one's surprise, the show's high-octane energy propelled onto our screens like Usain Bolt out of the starting blocks. In the first few seconds of the first episode, we're not only introduced to AC-12's latest adversary, Kelly Donaldson's DCI Joanne Davidson, but we're also brought into the middle of an ongoing, high-profile murder investigation. The episode had everything we've come to know and love from Line of Duty [2], placing doubts and questions into our heads about characters old and new, with the most burning question arising when DCI Davidson loses her cool, calm, collected head as she tries to uncover the identity of the "CHIS" who offered up intel relating to the unsolved murder of journalist Gail Vella [3] — because what in the world is a "CHIS"?

DCI Davidson mentions "CHIS" in the first 30 seconds of episode one, and at the mention of this new acronym, Twitter immediately gathered together in a collective "huh"?, shifting its focus from trying to piece together different snippets from the episode to figuring what the abbreviation stood for (Covert Human Intelligence Source, in case, like us, you were confused). Never one to pander to its audience, Line Of Duty has taken a strict policy of not dumbing down police patter for its civilian audience. To save the remaining episodes from becoming a circus of watch-pause-Google-play-repeat, here is your ultimate jargon-busting guide to the rest of the Line of Duty lingo.

General Police Acronyms

:

AC-12: Anti-Corruption Unit 12
ARU: Armed Response Unit
ARV: Armed Response Vehicle
B&E: Breaking and Entering
Blue-on-blue: The accidental shooting or injuring of an officer by another
CHIS: Covert Human Intelligence Source
CID: Criminal Investigation Department
CIS: Crown Investigation Department
CPS: Crown Prosecution Service
DIR: Digital Interview Recorder
DPS: Directorate of Professional Standards
DVU: Domestic Violence Unit
IC: Identification Codes
IC9: Unknown
IRV: Incident Response Vehicle
LEO: Local Enforcement Officer
LIO: Local intelligence officer
MIT: Murder Investigation Team
MoPi: Management of Police information
NCPA: No Cause for Police Action
NCS: National Crime Squad
NDIU: National Drugs Intelligence Squad
OCG: Organised Crime Group
PNC: Police National Computer
PR: Police Regulations
Reg 15: Regulation 15 Notice. This notifies an officer that they will be investigated following a complaint made against them.
RTC: Road Traffic Collision
SCG: Serious Crime Group
Sitrep: Situation report
SOCA: Serious and Organised Crime Agency
TA: Tactical Advisor

Police Rankings:

ACC: Assistant Chief Constable
CC: Chief Constable
DC: Detective Constable
DCC: Detective Chief Constable
DCI: Detective Chief Inspector
DCS: Detective Chief Superintendent
Det Supt: Detective Superintendent
DI: Detective Inspector
DS: Detective Sergeant

Police Roles:

AFO: Authorised Firearms Officer
CSE: Crime Scene Examiner
FI: Forensic Investigator
FLO: Family Liaison Officer
FME: Forensics Medical Examiner
PCSO: Police Community Support Officer
SFC: Strategic Firearms Commander
SIO: Senior Investigating Officer
UCO: Undercover Officer
TFC: Tactical Firearms Officer
TFU: Tactical Firearms Unit
UCO: Undercover Officer

It's a lot to take in, but we will definitely sleep better at night now that the CHIS mystery has been cleared up — such was the social media furore over it. Simply put, it's a police informant. The CHIS in question during the episode met a grizzly end, and now that everyone's police-related vocabulary has been sufficiently expanded, the focus can be returned to conspiracy theories and practicing armchair detective work. Why did DCI Davidson want to find out who he was so badly? Why did she say to DS Buckells (Nigel Boyle) that the only way "this can go the way we want" if if the CHIS is found? No doubt the talented team of actors and writers will unfold the reasons in the coming weeks.