Today, May 2, is the anniversary of Oliver Otis Howard’s worst day on a battlefield. (Although losing his arm on the Peninsula must have been pretty bad, too.) On May 2, 1863, General Thomas J. “Stonewall” Jackson unleashed a devastating flank attack on Howard’s XI Corps during the Battle of Chancellorsville. The attack came as a complete surprise to General Howard, although it should not have. Howard had received warnings from various sources that something was happening on his unprotected right—warnings he disregarded.

Here’s a portion of what I wrote in Maine Roads to Gettysburg about Howard’s terrible day.

As the sun rose on May 2, Joe Hooker arrived along the XI Corps line to take a look at its defenses. He appeared impressed. “How strong! How strong,” he said. Yet he must have developed some reservations, for later in the day he had an order sent to Howard, warning him that his preparations had been made with the idea that the enemy would make a frontal attack. “If he should throw himself upon your flank,” said Hooker’s message, the commanding general “wished you to examine the ground and determine upon the position you will take in that event, in order that you may be prepared for him in whatever direction he advances.” Hooker advised Howard to keep “heavy reserves well in hand to meet this contingency. We have good reason to suppose that the enemy is moving to our right. Please advance your pickets as far as may be safe, in order to obtain timely information of their approach.” Hooker then sent a second, similar message to both Howard and Henry Slocum, whose XII corps was next in the Union line. “The right of your line does not appear to be strong enough,” Hooker warned. “No artificial defenses worth naming have been thrown up, and there appears to be a scarcity of troops at that point, and not, in the general’s opinion, as favorably posted as might be.”

Sometime around noon, Howard complained of fatigue and said he wanted to catch some sleep. He instructed division commander Carl Schurz to wake him if any urgent dispatches arrived. When Hooker’s directive to watch the flank arrived, Schurz said, he immediately took the message to Howard. The second warning arrived shortly afterwards. Howard said he did not recall seeing any such messages. In any event, he claimed, he had gone ahead on his own initiative and done what the message had instructed to protect his flank.

That would have surprised Schurz, who said he pointed out to Howard the weakness of his right. “Do you not think it certain that the enemy, attacking from the west, will crush Gilsa’s two regiments, which are to protect our right and rear, at the first onset?” he asked. “Is there the slightest possibility for him to resist?”

As Schurz remembered it, all Howard had to say was, “Well, he will have to fight.”

The Federals had received their first hint that something was up around eight o’clock that morning, when a long column of Confederates became visible to the south through a gap in the trees near a place called Catherine Furnace. The reports reached David Birney, who commanded a division in the III Corps, and he sent word to Dan Sickles, his corps commander. Sickles ordered his artillery to shell the enemy soldiers.

Eager for a fight, Sickles had Hiram Berry send out two of his regiments to see what the enemy was up to, and he asked Hooker for permission to do more. With Hooker’s blessing, Sickles advanced Birney’s and Amiel Whipple’s divisions, with Hiram Berdan’s sharpshooters as skirmishers. By the time Sickles reached Catherine Furnace, almost all the Confederate column had marched off into the woods, leaving only the 23^rd Georgia behind to be captured. It was possible that Jackson was marching to attack the army’s right; it was also possible that Lee was retreating. Hooker apparently believed the second interpretation, and when Howard returned to his headquarters later in the day, he did, too.

Carl Schurz did not share that optimistic interpretation. He rode over to Dowdall’s Tavern to tell Howard he thought Jackson was preparing to attack their right—he even stopped along the way to tell Capt. Hubert Dilger to find some good westward-facing positions for his artillery battery. Howard would have none of it. Lee was retreating, he said. “I was amazed at this belief,” recalled Schurz. “Was it at all reasonable to think that Lee, if he really intended to retreat, would march his column along our front instead of away from it, which he might have done with far less danger of being disturbed?” Howard remained unconvinced.

Increasingly desperate, Schurz moved three of his regiments so they would be better positioned to resist an attack from the west. Howard, he said, did not object. Other than that, along with the digging of some shallow entrenchments and a movement of the artillery reserve, nothing else was done to improve what Schurz called the XI Corps’ “absurdly indefensible position.” It was made even more difficult to defend when Hooker asked Howard to send Barlow’s brigade forward to support Sickles. Howard, who had intended to keep Barlow as his reserve, “deemed it of sufficient importance” to accompany the brigade on Sickles’s expedition personally.

The blow fell sometime after 5:00 p.m. Jackson’s men had indeed headed south at Catherine Furnace, but only until they reached a road that ran north toward the Orange Turnpike to the west of the XI Corps’ position. Jackson placed his men—the divisions of Robert Rodes, Raleigh Colston, and A. P. Hill—in long lines of battle that extended north and south of the turnpike and easily overlapped the unsuspecting XI Corps off to the east. Then Jackson ordered his men forward. The Rebels pushed their way through the woods and thickets that separated them from Howard’s mostly unsuspecting men. Animals fled the lines of humans forcing their way through the tangled growth and burst out of the woods to scamper through the camps of Howard’s men, many of whom had stacked their arms and were playing cards or cooking food. There was the sound of gunfire, the warning shots of the pickets, and then Jackson’s soldiers burst out of the woods like a whirlwind. The surprise was so complete, said one soldier from the 153^rd Pennsylvania, in von Gilsa’s brigade, “some of our men were shot in the back while sitting on their knapsacks.”

Howard had just returned to his headquarters from his expedition with Barlow when he heard “the ceaseless roar of the terrible storm” from the right. He sent messengers to find out what was happening and rode out to find a central position behind Schurz’s lines. It wasn’t long before men came rushing past him in a panic. Howard compared it to “all the fury of the wildest hailstorm.” “It was a terrible gale!” he recalled, “the rush, the rattle, the quick lightning from a hundred points at once; the roar, redoubled by echoes through the forest; the panic, the dead and dying in sight and the wounded straggling along; the frantic efforts of the brave and patriotic to stay the angry storm!” Howard made some frantic attempts to reform his line to face this new threat, but it was no use. It didn’t help that the general’s horse, caught up in the panic, threw its rider to the ground. One of his aides, Capt. Frederick Dessaur, was shot and killed. Howard dashed about the battlefield, trying to stem the flood, to little effect. “Such a mass of fugitives I haven’t seen since the prior battle of Bull Run,” Howard wrote his wife. Years later he told a reporter that he “wanted to die. It was the only time I ever weakened that way in my life, before or since; but that night I did all in my power to remedy the mistake, and I sought death everywhere I could find an excuse to go on the field.”

Adapted from Maine Roads to Gettysburg, which is available for purchase now. You can find it on Amazon.com, BarnesandNoble.com, or at any fine bookseller near you.