| AA | - | Always Afloat |
| AAAA | - | Always Afloat, Always Accessible |
| AAOSA | - | Always Afloat Or Safe Aground |
| AAR | - | Against All Risks |
| AARA | - | Always Accessible or Reachable on Arrival |
| AB | - | Able Seaman |
| ABS | - | American Bureau of Shipping |
| AC | - | Alternating Current (electricity) |
| ACV | - | Air Cushion Vehicle |
| AD | - | Area Differential |
| ADF | - | Automatic Direction Finder |
| AF | - | Anti-Fouling |
| AFFF | - | Aqueous Film Forming Foam |
| AFRA | - | Average Freight Rate Assessment |
| AG | - | Arabian Gulf |
| AGW | - | Actual Gross Weight |
| | - | All Going Well |
| AHTS | - | Anchor Handling Tug and Supply Vessel |
| AIS | - | Automatic Identification System |
| ALERT | - | Automatic Life-saving Emergency Radio Transmitter |
| ALRS | - | Admiralty List of Radio Signals |
| AMSL | - | Above Mean Sea Level |
| AMVER | - | Automated Mutual Assistance Vessel Rescue System |
| AMWELSH | - | Americanised Welsh Coal Charter party |
| ANERA | - | Asia-North America Eastbound Rate Agreement |
| ANOP | - | Articles Not Otherwise Provided for |
| ANSI | - | American National Standard Institute |
| AO | - | Awaiting Orders |
| | - | And Other |
| AOB | - | Any One Bottom |
| AOH | - | After Office Hours |
| AOLOC | - | Any One Location |
| AOR | - | Atlantic Ocean Region |
| AOS | - | Any One Steamer |
| AOV | - | Any One Vessel |
| AP | - | All Purposes |
| | - | Additional Premium |
| | - | Aft Perpendicular |
| API | - | American Petroleum Institute |
| APS | - | Arrival Pilot Station |
| APT | - | Aft Peak Tank |
| ARA | - | Antwerp - Rotterdam - Amsterdam |
| ARPA | - | Automatic Radar Plotting Aid |
| A/S | - | Alongside |
| ASAP | - | As Soon As Possible |
| ASBA | - | The Association of Shipbrokers and Agents (USA) Incorporated, New York |
| ASCII | - | American Standard Code for Information Interchange |
| ASPW | - | Any Safe Port in the World |
| ASTM | - | American Society of Testing & Materials |
| ATA | - | Actual Time of Arrival |
| ATD | - | Actual Time of Departure |
| ATDN | - | Any Time Day & Night |
| ATDNSHINC | - | Anytime Day/Night Sundays & Holidays Included |
| ATK | - | Aviation Turbine Kerosene |
| ATS | - | All Time Saved |
| ATSBE | - | All Time Saved Both Ends |
| ATSDO | - | All Time Saved Discharging Only |
| ATUTC | - | Actual Times Used To Count |
| AUV | - | Autonomous Underwater Vehicle |
| AVGAS | - | Aviation Gasoline |
| AVR | - | Automatic Voltage Regulator |
| AVTAG | - | Aviation Turbine Gasoline |
| AWIWL | - | Always Within Institute Warranty Limits |
| AWVNS | - | Always Within Vessel's Natural Segregation |
| AWRI | - | Additional War Risk Insurance |
