What was the name of the first steamship built for transatlantic service?

The SS Great Western was the first steamship built specifically for transatlantic service.

Designed by Isambard Kingdom Brunel, Great Western was constructed for the Great Western Steamship Company’s planned Bristol–New York route. She was a large wooden side-wheel paddle steamer, strengthened with iron and fitted with auxiliary sails. Her size caused controversy, but Brunel argued that a larger hull would carry passengers and fuel more efficiently across the Atlantic.

The ship was launched in 1837 and began her maiden voyage in April 1838. Although the smaller Sirius reached New York first on that particular contest, Sirius had been adapted from an existing coastal packet. Great Western was purpose-built for regular Atlantic crossings, which is why it holds the canonical answer to this question.

Great Western completed 45 Atlantic crossings during eight years of service. It was later used on routes to the West Indies and South America before being sold for scrap in 1856. Brunel’s later SS Great Britain is often confused with it, but that ship was a newer iron-hulled screw steamer.