If it's an 'atlantic crossing based on true story', it could be a story of survival and perseverance. There are so many stories of ships facing storms, running out of supplies, and yet still making it across the vast ocean. It could also be about the cultural exchange that happened as a result of these crossings. People from different continents met and influenced each other's cultures, which is an important aspect of any true story related to crossing the Atlantic.
The 'atlantic crossing based on true story' might be a tale of adventure. It could be centered around a particular ship or group of people. For instance, it could be about the first transatlantic flight which was also a form of 'atlantic crossing' in a sense. Or perhaps it's about the slave trade, which was unfortunately a very real and dark part of Atlantic crossings in history.
Well, it could be about a lot of things. Maybe it's about a ship's journey across the Atlantic. It might involve real historical events like the early voyages of discovery, or it could be a story about people migrating across the Atlantic in difficult times. Without more context, it's hard to say exactly.