I've been posting some pictures of Orchard Knob but haven't really provided any background yet, this should alleviate that problem somewhat.
On the morning of November 23rd Grant learned from Confederate deserters that Bragg's army was preparing for some movement, most likely a retreat. Grant ordered Thomas to make a reconnaissance to see if Bragg was indeed leaving. If two men are better than one then 26,600 men are better than two, so Thomas sent six divisions forward for reconnaissance. The target was Orchard Knob, a 100 foot high hill about 2,100 yards east of Fort Wood. At around 2 P.M. the advance began.
The 24th and 28th Alabama of Brigadier General Arthur M. Magnigault's brigade held the picket line on Orchard Knob. These 634 men covered an 800 yard front and faced odds of nearly 42 to 1. The 24th Alabama saw the advance and pulled out without orders. The 28th Alabama stayed believing that they would soon be supported; Magnigault later denied ever promising support. The 28th Alabama's view of the 24th Alabama on their right was blocked by a timbered knoll so they did not realize that they were all alone. Hazen's brigade came upon the 28th Alabama and the 41st Ohio charged without orders. The 41st Ohio lost 117 of 447 men in the short fight as the rest of Hazen's brigade soon outflanked the 28th Alabama, capturing 146. This fighting ended at about 2:20 P.M.
The initial orders for the reconnaissance had been to return to Fort Wood following the completion of the mission, but after seeing the position they had gained Thomas' men dug in at the new spot. The Union high command initially believed that a Confederate counterattack would be soon in coming but the afternoon dragged on with only a light barrage from Missionary Ridge. It was still not clear if Bragg's army intended to fight or flee. As a skirmish Orchard Knob achieved little more than creating 400 casualties but it convinced Bragg to recall Cleburne's men, who had been recently ordered to go to Longstreet's aid in east Tennessee.
That evening Magnigault was ordered to retake Orchard Knob (now with 6,000 entrenched Federals on it) with his brigade, which probably numbered 1200 to 1500 men. He considered it a big mistake but made preparations to follow his orders. When he protested to his division commander, Brigadier General Patton Anderson, he was told that the enemy's numbers were exaggerated. Magnigault had gone back to his brigade to order it forward when a message arrived from Anderson canceling the attack. It seems that the division officer of the day informed Anderson that at least 10,000 Federals were at Orchard Knob.
When Major General Patrick R. Cleburne's men arrived back behind Missionary Ridge, Bragg had them stop there to be a reserve. By this time Bragg had conceded the overall initiative of attack to the Union.