First Steam Ship to cross the Atlantic
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The first steam vessel to cross the North Atlantic was the side-wheeler 
SAVANNAH, which sailed from Savannah, Georgia, on 22 May 1819, anchored 
off the Tybee Light, and sailed thence at 5 A.M., on 24 May.  She anchored 
at Liverpool at 6 P.M., on 20 June 1819, after a voyage of 29 days 4 hours 
from Savannah.  She then proceeded to Helsingor (Elsinore), Stockholm, and 
St. Petersburg, where she remained about a month.  She returned to 
Savannah without passengers or cargo, via Copenhagen and Arendal, Norway, 
arriving on 30 November 1819.

The first steam vessel to cross from Great Britain to North America was 
the side-wheeler CAPE BRETON, which sailed from Plymouth on 21 June 1833, 
and arrived at Sydney, Nova Scotia, on 4 August, after a voyage of 44 
days.

The first sailing of what became the first regular transatlantic service 
between Great Britain and the United States was by the side-wheeler 
SIRIUS, chartered to the British & American Steam Navigation Co, which 
sailed from London on the afternoon of 28 March 1838, and from Cork at 10 
A.M. on 2 April.  She sighted land on the afternoon of 22 April, and 
anchored off the Battery, New York, early the next morning.  A few hours 
later, she was joined by the side-wheeler GREAT WESTERN, of the competing 
Great Western Steamship Co, the first steamer built specially for the 
North Atlantic service, which had sailed from Bristol on 8 April 1838.

Both the British & American Steam Navigation Co and the Great Western
Steamship Co were of short duration, the former suspending operations in
1841, the latter in 1846.  Long-term success required a government mail 
contract, which was first obtained by Samuel Cunard for his British & 
North American Royal Mail Steam Packet Co (the Cunard Line) in 1840.

For the early history of steam navigation across the North Atlantic, see
most conveniently Noel Reginald Pixell Bonsor, _North Atlantic Seaway; 
An Illustrated History of the Passenger Services Linking the Old World with
the New_ (2nd ed.;  Jersey, Channel Islands: Brookside Publications), vol.
1 (1975), in particular, pp. 39-71.