Explanation: Wiki puts it better than I could:

The regiment’s most famous action occurred during the second day’s fighting at Gettysburg, when Major General Winfield Scott Hancock ordered the 1st Minnesota, composed of roughly 250 men, to charge into a brigade of roughly 1,200 men belonging to James Longstreet’s corps and Richard H. Anderson’s Division. Although the regiment was outnumbered by a ratio of at least 5 to 1, charging was Hancock’s only opportunity to buy time for Union reinforcements to arrive. One survivor stated afterward that he expected the advance to result in “death or wounds to us all”.[9] The regiment immediately obeyed the order and Hancock was reportedly amazed at the unit discipline, valor, and the tremendous casualties taken in carrying out his order. This action blunted the Confederate attack and helped preserve the Union’s precarious position on Cemetery Ridge at the end of the second day of the battle.

Their charge bought the Union the time it needed for reinforcements to be brought up. During the charge, 215 of the 262 who made the charge became casualties within five minutes (47 killed, 121 wounded, 90 missing). That included the unit commander, Col. William Colvill, and all but three of his captains.

The 1st Minnesota’s flag lost five flag bearers, each man dropping his weapon to carry it on. The 47 survivors rallied back to General Hancock under the command of their senior surviving officer, Captain Nathan S. Messick. The 82% casualty rate stands as the second largest loss by any surviving U.S military unit in a single day’s engagement. The unit’s colors are displayed in the rotunda of the Minnesota Capitol for public appreciation.[14]