Final answer:
A Major Marine Casualty involves significant impacts from marine incidents, with response actions focused on rescue, containment, and investigation.
Step-by-step explanation:
A Major Marine Casualty refers to an incident involving a vessel or its crew that results in a significant impact, such as a substantial loss of life, major damage to property, or serious disruption to commerce or navigation. In responding to such events, the basic actions typically include prompt search and rescue operations, containment and mitigation of environmental harm, and investigation to determine the cause. Safety measures, communication procedures, and coordination with relevant authorities are crucial components of the response plan.