Sometimes losing is instrumental to learning how to win. Sometimes losing is just a humiliating defeat.
The United States acquired Florida in 1821. In 1835, a detachment of over 100 soldiers was dispatched to police the local Seminole tribes. The entire detachment was wiped out. That’s a loss rate of 100 percent—a defeat not matched any other major engagement.
Sure there have been other really bad days for Americans in battle, but nothing like what became known as the “Dade Massacre.”
In contrast, at least 14 people, for example, survived the Battle of the Alamo (1836) and that battle really doesn’t count anyway because Texas didn’t become a state till 1945.
All 210 of Custer’s command did die at the Little Big Horn (but a horse survived and 60-70 horses were captured). Still, the battle was part of a bigger battle including the Battle of the Rosebud (1876), so the entire unit in the campaign was not wiped out.
Biggest U.S. loses in a single campaign was the Meuse-Argonne Offensive (September 26, – November 11, 1918), over 26,000 killed in action, but then again one million doughboys fought in this action.
The largest American loses in the a single battle was probably Gettysburg (1863). Deaths numbered almost 8,000 (but that included troops from both sides and the fight last three days).
No. The opening fight of the Second Seminole War seems to be the dubious winner of the most disastrous campaign in U.S. military history.