The Battle of Fort Donelson on the Cumberland River near Dover, Tenn., marks the first major Union battlefield victory of the Civil War, 150 years ago this week in 1862.

Federal gunboats on Feb. 14, 1862, began exchanging heavy fire with big Confederate artillery guns set high up on the river bluff. But the gunboats suffered such damage that their decks ran with blood and they were soon forced to withdraw, denying Union Brig. Gen. Ulysses S. Grant the speedy victory he had hoped to achieve.

The next day, Grant sent in ground troops, fighting a pitched battle with the fort’s Confederate defenders before his soldiers are forced to retreat. Confederate defenders mistakenly believed they had won the confrontation. But then Grant surprises them with a counterattack, taking back lost ground and setting the stage for a Union victory. Some 2,000 Confederate fighters slipped away before Grant captured those defenders still remaining.

Asked for his terms of surrender, Grant bluntly and famously replied: “ No terms except an unconditional and immediate surrender can be accepted.” The remaining Confederates gave up the fight as Fort Donelson became the first sizable land victory for the North in the Civil War.

At Fort Donelson, “ Unconditional Surrender” Grant would gain hero status. The victory would help secure Grant a promotion to major general and begin forging a destiny that would take him on to become eventual commander of all the Union armies.