"Embalmed beef" was the name that caught on in the media (well, the newspapers) for the badly-preserved meat served to American soldiers during the Spanish-American War. It was first used by Nelson Miles, commanding general of the U.S. Army, when complaining after the war to President William McKinley's investigating commission about the supplies that had been procured for the army.

Previously, soldiers had done their own cooking and gotten hold of their own supplies in the U.S. Army. However, in this case, they were going to be fighting in Cuba and the Philippines and would have trouble bringing cattle from home to string along behind the troops, and the wooden crates of hard-tack biscuits did not keep at all well in tropical climates. It required legislation in Congress to allot money to hire army cooks (and some military leaders opposed the cooks' hiring, thinking the soldiers would be too pampered). Charles Egan, commissary general, did his best to try and get appropriate supplies; refrigeration was not too practical, so canned beef was ordered -- seven million pounds of it. It made an adequate stew with the addition of a few vegetables, and it would keep.

However, the soldiers in the field didn't get stews -- they got cold, unsalted beef straight from the cans, because there were hardly any saucepans available for the army cooks to do anything else with it. Teddy Roosevelt called his men babies for disdaining the slimy stuff, but then later he tried it and found himself repulsed too. Cans were reported that contained gristle, bits of rope, maggots, or poisonous preservatives, or had been spoiled by the heat. This was most likely a very small minority of cans, sent out by packers who needed to make up a very large order very quickly. But some men did die of food poisoning, and Nelson Miles did his best to ride the scandal of bad food sent out to the defenders of the nation's interests, with the newspapers jumping on the bandwagon.

McKinley's commission did not find widespread contamination even after samples of the canned beef were sent for lab testing. Miles kept on trying to press his charges, hoping for the Democratic presidential nomination against the Republican administration. However, the fact that he had only pointed this out after the war, and not while his soldiers were actually suffering from the bad food they were supplied with, caused him problems. His enemies suggested that he was trying to get back at the meat-packing industry for the humiliation of his troops' failure to control riots outside Chicago packinghouses a few years earlier. His political career folded, but the idea of "embalmed beef" remained associated with the Spanish-American war. It did spur the U.S military to make better arrangements for provisions in future conflicts, and along with publication of Upton Sinclair's The Jungle and other exposes in the next few years, led to pure food and drug legislation in the United States.

Sources:
Carlson, Laurie Wynn. Cattle: An Informal Social History. Chicago: Ivan R. Dee, 2001.
http://www.natick.army.mil/warrior/97/nov/thanks.htm
http://www.myhistory.org/historytopics/articles/pure_fd_dg_act.html