What did 19th-century sailors call the heavy biscuits that sustained them on long journeys?

Answer 1

Hardtack (US) or Hard Tack (UK) :

"The first thing to know is that “ship’s biscuit” was not called “hard tack” until long after the War of 1812. In Britain and America during the Revolution and the War of 1812, it was officially and unofficially known as “Sea Biscuit,” “Ship’s Biscuit,” “Biscuit,” “Ship’s Bread,” “Hard Bread,” and “Bread”--and no doubt on occasion other less printable names now lost to history--but not “hardtack.”"

"In the early 19th century “tack” was a common word for “a cattle pasture for hire,” perhaps so-called from the vessel-like wandering of the cattle as they grazed. Naturally, “tack” soon became vulgar slang for any coarse cheap food. However, the term “hard tack” only came into common sailor use around 1835, moving into mainstream American English during the Whaling boom of the 1840s. Ship’s bread was also sometimes known as “pantiles” by mid 19th century British sailors."

"Not only did the name change, but so did biscuit: Civil War hardtack actually was very different from War of 1812 hard bread. Just as military science morphed 1918’s “Trench Ration” into 1944’s “C-Rations,” so was 1812’s “ship’s bread” transformed 1861’s “hardtack”: By the Civil War, US issue “hardtack” (though officially still called “hard bread”) was smaller, square, and often of white flour—altogether different from the “hard bread” issued to British and American soldiers and Sailors in the War of 1812."

"Biscuits, Bugs, & Broadsides -- or -- Everything You Ever Wanted to Know About Hard Tack", Mark Hilliard, 1812 US Marines & Navy : http://www.1812usmarines.org/Biscuits,%20Bugs,%20&%20Broadside.doc

Answer 2

Sailors Biscuits

Answer 3

Hardtack

Answer 4

Hardtack. Read about it - and other names for it - here:
http://en.wikipedia.org/wiki/Hardtack

Answer 5

hard tack...