Maritime Acronyms in Plain English

By Captain Mike · 50 years at sea · former MITAGS faculty
October 2026

New mariners run into a wall of letters: MMC, TWIC, STCW, QMED, RFPNW, OUPV. You don't need to memorize them all. Look them up as you meet them, and learn the handful that apply to the job you want.

Credentials and endorsements

Acronym	Stands for	What it means
MMC	Merchant Mariner Credential	The Coast Guard credential (a passport-style book) that shows every endorsement you hold. More →
TWIC	Transportation Worker Identification Credential	A TSA-issued ID card for unescorted access to secure areas of ports and vessels. More →
STCW	Standards of Training, Certification and Watchkeeping	The international convention behind the STCW endorsements on your MMC. More →
OS	Ordinary Seaman (now Ordinary Seafarer)	The entry-level deck rating. More →
AB	Able Seaman (now Able Seafarer)	The qualified deck rating above OS. More →
RFPNW	Rating Forming Part of a Navigational Watch	STCW endorsement for deck ratings who stand watch on seagoing ships. More →
RFPEW	Rating Forming Part of an Engineering Watch	STCW endorsement for engine ratings who stand watch. More →
QMED	Qualified Member of the Engine Department	Engine ratings above Wiper, such as Oiler or Electrician. More →
OUPV	Operator of Uninspected Passenger Vessels	The "six-pack" license: up to six paying passengers. More →
PIC	Person in Charge	The person in charge of a cargo transfer; also Tank Vessel-PIC and Tank Barge-PIC endorsements. More →
DL / LG	Dangerous Liquids / Liquefied Gases	The two cargo categories on tank vessel endorsements. More →
PSC	Proficiency in Survival Craft	STCW lifeboat endorsement. (In port-state work, PSC also means Port State Control.) More →
OICNW	Officer in Charge of a Navigational Watch	The STCW endorsement for deck watch officers, such as Third and Second Mate.
OICEW	Officer in Charge of an Engineering Watch	The STCW endorsement for Third and Second Assistant Engineers. More →
DDE	Designated Duty Engineer	An engineer endorsement for smaller vessels, limited by horsepower.
3/M, 2/M, C/M	Third, Second, Chief Mate	Deck officer ranks below Master. More →
3A/E, 2A/E, 1A/E, C/E	Third, Second, First Assistant Engineer; Chief Engineer	Engine officer ranks. More →
TOAR	Towing Officer Assessment Record	A record of towing skills signed off aboard, needed for towing officer endorsements. More →

Training and courses

Acronym	Stands for	What it means
BT	Basic Training	The four-part STCW safety course. More →
PST	Personal Survival Techniques	Part of Basic Training.
FPFF	Fire Prevention and Fire Fighting	Part of Basic Training.
EFA	Elementary First Aid	Part of Basic Training.
PSSR	Personal Safety and Social Responsibilities	Part of Basic Training.
AFF	Advanced Fire Fighting	Firefighting leadership course required for many officers. More →
ARPA	Automatic Radar Plotting Aid	Radar equipment, and the STCW course in using it. More →
ECDIS	Electronic Chart Display and Information System	Electronic charting system, and the course for it.
BRM	Bridge Resource Management	Teamwork and decision-making on the bridge.
ERM	Engine Room Resource Management	The engine-room version of BRM.
GMDSS	Global Maritime Distress and Safety System	The international distress-radio system, and the radio operator endorsement.
VPDSD	Vessel Personnel with Designated Security Duties	STCW security training for crew with security duties.
CPR	Cardiopulmonary Resuscitation	Required with First Aid for many small-vessel licenses.

Forms, records and applying

Acronym	Stands for	What it means
CG-719B	Application for MMC	The Coast Guard credential application form.
CG-719K	Medical certificate application and exam report	The medical exam form. CG-719K/E is the short version for entry-level ratings. More →
CG-719P	DOT/USCG Periodic Drug Testing Form	Proof of a passed drug test.
CG-719S	Small Vessel Sea Service Form	Documents sea time on smaller vessels, one vessel per form. More →
ATT	Approval to Test	NMC approval listing the exam modules you must pass. More →
TOSS	Transcript of Sea Service	Coast Guard military sea-service record. More →
HOA	History of Assignments	Navy sea-service record. More →
DD-214	Certificate of Release or Discharge from Active Duty	Military discharge form. Not accepted as proof of sea service.
SF-180	Standard Form 180	The form to request military records from the National Archives.
DOI	Declaration of Inspection	The pre-transfer checklist signed before a cargo transfer.

Agencies, rules and organizations

Acronym	Stands for	What it means
USCG	United States Coast Guard	Issues and regulates mariner credentials.
NMC	National Maritime Center	The Coast Guard office that evaluates applications and issues MMCs.
REC	Regional Exam Center	Coast Guard offices where you take written exams.
OCMI	Officer in Charge, Marine Inspection	The local Coast Guard official responsible for vessel inspection in a zone.
CFR	Code of Federal Regulations	U.S. regulations. Title 46 covers shipping and mariner credentials. More →
NVIC	Navigation and Vessel Inspection Circular	Coast Guard guidance explaining how rules are applied. More →
MSM	Marine Safety Manual	The Coast Guard's internal policy manual.
TSA	Transportation Security Administration	Issues the TWIC.
DOT	Department of Transportation	Sets the drug-testing procedures mariners follow.
IMO	International Maritime Organization	The UN agency behind STCW and SOLAS.
SOLAS	Safety of Life at Sea	The main international ship-safety convention.
MARAD	Maritime Administration	U.S. Department of Transportation agency that runs the U.S. Merchant Marine Academy.
USMMA	U.S. Merchant Marine Academy	The federal academy at Kings Point, New York. More →
MSC	Military Sealift Command	Navy command that crews government ships with civilian mariners. More →
SIU, MM&P, AMO, MEBA, SUP	Maritime unions	Seafarers International Union; Masters, Mates & Pilots; American Maritime Officers; Marine Engineers' Beneficial Association; Sailors' Union of the Pacific. More →

Vessels and measurements

Acronym	Stands for	What it means
GRT	Gross Register Tons	The U.S. measurement used on most national endorsements. More →
GT	Gross Tonnage	The international (ITC) measurement used on STCW endorsements. More →
OSV	Offshore Supply Vessel	Vessels that support offshore oil, gas and wind work.
MODU	Mobile Offshore Drilling Unit	Drilling rigs and drillships.
ATB / ITB	Articulated / Integrated Tug-Barge	A tug locked into a notch in the stern of a barge.
LNG / LPG	Liquefied Natural Gas / Liquefied Petroleum Gas	Gas cargoes carried under the LG category.
COI	Certificate of Inspection	The Coast Guard certificate for an inspected vessel, including its required crew.
DP / DPO	Dynamic Positioning / DP Operator	Computer-controlled station keeping, common offshore.
GIWW	Gulf Intracoastal Waterway	The inland waterway along the Gulf Coast.
HP	Horsepower	Propulsion power, which limits many engineer endorsements.

THE CAPTAIN SAYS…

Don't try to learn every acronym before your first job. Learn the ones on your own credential and the ones your crew uses every day. The rest come with time at sea.

Not finding one? Use the site search at the top of the page, or start with Start Here.

For information only. Definitions are simplified for beginners; check the official source for the legal meaning.