The S.S. United States has just been tossed a life preserver.

In its 1950s heyday, the historic ship — the world’s fastest luxury liner — dashed across the Atlantic carrying royalty and immigrants alike to American shores. But for nearly a half century now the “Big U,” as the ship is known, has been docked, collecting barnacles and rust after jet travel lured away all the customers.

Now, however, there is a chance the S.S. United States may sail again, after Crystal Cruises, a luxury travel company, signed a purchase option for the ship. Just months earlier, preservationists almost had to scrap the Titanic-size vessel as their funds dwindled.

For Crystal it would be the latest addition to an ambitious and sometimes unconventional collection of luxury travel offerings — including excursions by personal submarine, and plans for a “cruising in the sky” luxury jumbo jet. It could also be among the most difficult.

A makeover of the ship could cost from $700 million to $800 million, according to Crystal’s chief executive, Edie Rodriguez, potentially a little less than building something similar from scratch. Under terms of the agreement, the company will cover the approximately $60,000-a-month cost of caring for the ship for nine months while it does a feasibility study.