Final answer:
Pre-trial confinement aboard a naval vessel at sea, particularly for naval forces or the militia during wartime or public danger, is exempt from the requirement of a Grand Jury indictment. The Supreme Court has upheld certain powers to detain without standard legal processes, but habeas corpus rights allow for the review of the legality of detentions.
Step-by-step explanation:
The question asks how long pre-trial confinement may continue aboard a naval vessel at sea. According to the Fifth Amendment and a collection of legal precedents, this confinement can continue on the grounds of national security during times of war or public danger. Specifically, individuals serving in the land or naval forces, or the Militia, during these times, are exempt from the requirement of a Grand Jury indictment before being held for a capital or infamous crime. This is a reflection of the special jurisdiction military forces are subject to, which is governed by the Uniform Code of Military Justice.
Further, the legal basis for detaining individuals, such as enemy combatants, has been supported by the Supreme Court, which acknowledges the government's power to detain without the standard civilian legal processes in specific circumstances, like in the case of Rasul v. Bush. However, due process requirements may differ for citizens versus non-citizens and within the United States versus outside. Lastly, the writ of habeas corpus is a critical right that allows the legality of detention to be reviewed by a court, and this right can be suspended only in cases of rebellion or invasion where public safety requires it.