The U.S. Coast Guard (USCG) has primary responsibility for investigating marine accidents in U.S. territorial waters or involving U.S. ships. For significant incidents, they often work jointly with the National Transportation Safety Board (NTSB). The most detailed, complete, and easy to understand reports on major marine accidents are the NTSB's Marine Accident Reports.
USCG
Coast Guard investigations tend to be focused on the need for new regulations and on the enforcement of existing regulations, including the suspension or revocation of the licenses of mariners involved in the accident. If negligence or misconduct is discovered, they may refer a case to the Justice Department for criminal prosecution.
When the USCG completes an investigation they issue a Report of Investigation (ROI). Not all ROIs are available to the public, but those that are can be found on the website of the Office of Investigation and Casualty Analysis.
Brief summaries of the current state of a USCG investigation can be found by searching for Incident Investigation Reports in the Maritime Information Exchange.
NTSB
The NTSB will participate in marine casualty investigations when they are considered to be "major." This includes accidents that resulted in the loss of six or more lives, the loss of a vessel of more than 100 gross tons, property damage estimated to be above $500,000, or which the Commandant of the Coast Guard and the NTSB jointly decide constitutes a serious threat to life, property, or the environment. The NTSB website contains a description of its investigation process. NTSB investigations and reports focus on safety culture and potential safety inprovements. They do not consider criminal behavior or attribute fault to specific individuals or entities.
Completed investigations result in Marine Accident Reports. Each report has a webpage which has a right-hand sidebar summarizing the accident information and providing links to the investigation docket, a collection of all the documents that were created in the process of the investigation. The docket will typically include photocopies of the ship's log and other ship's paperwork, statements made by and interviews with crew members, and charts of the accident area.
Data for marine accidents that have occurred since 2010 are also searchable in the NTSB's CAROL database (which stands for Case Analysis and Reporting OnLine). The CAROL database is simply another way to navigate to the same Marine Accident Reports and investigation dockets.
