“Where was Ney?” That was the question on everyone’s mind at Ligny on the afternoon of 16 June 1815. Excellent staff work by the Prussians, and poor staff work by the French (massive traffic jam at Charleroi) allowed Blücher’s Prussians to outnumber Napoleon, 85,000 to 63,000. Nonetheless, Napoleon attacked and caused great damage to Blücher, particularly by his cannon which found the Prussian formations excellent targets. But he couldn’t destroy him without Ney. Ney had orders to seize Quatre Bras the night before, hold it with a minimum force and then march on Blücher’s right this morning. (Napoleon had no idea that the crossroads were not in French hands yet.) D’Erlon’s I Corps, closest to Napoleon, should have been there hours ago. Napoleon would send another order, this time directly to D’Erlon.
D’Erlon was still enroute to Quatre Bras, as per Ney’s orders. At those vital crossroads Ney was locked in a bitterly fought struggle where every time he thought he won, fresh British or Dutch units arrived. Ney had orders to take the crossroads the night before, and was in contact with Dutch units there since then, but for some reason lost to history, didn’t engage with his main force until the afternoon of the next day. Even though Ney started the battle much too late, the French could still destroy Wellington’s Anglo-Allied army if D’Erlon’s 20,000 men fell on Wellington’s left. When D’Erlon was about an hour from Quatre Bras and just about to move into his assault columns, Napoleon’s message arrived.
Napoleon’s plan was to defeat the British first, or at least fix them, then destroy the Prussians. So D’Erlon still marched to where he thought he was needed. Napoleon’s message changed that even though the British were not yet defeated. But Napoleon’s intent was to isolate and destroy one army and then the other. And that opportunity was there for the taking, just not in the same order as in the plan. To D’Erlon, it simply came down to a question of defying Ney or defying Napoleon. That wasn’t really a question.
Much to Ney’s astonishment, D’Erlon turned around and headed back the way he came… and missed both battles.
That night Blücher’s battered Prussians retreated from Ligny: thoroughly defeated, but not destroyed. It was close, though: over the night of 16-17 June, the Prussians suffered 28,000 desertions, mostly Saxons and Rhinelanders whom had previously fought for Napoleon. Nearly a third of Blucher’s army was gone. At Quatre Bras, Wellington, especially his Dutch, had a won a great victory, though it would go down in history as a defeat. The Anglo-Allied Army still held the field, but upon learning of Blucher’s retreat, Wellington fell back the next morning from the now untenable position. During these retreats, both armies were at their most vulnerable.
Napoleon allowed them to escape. He had just won his first victory since his abdication and indulged himself early on 17 June in those activities that endear commanders so much to their men: He visited the wounded, ensured their care, chatted with the troops, and toured the battlefield with his favorites. Although there is definitely a time and place for these things, the morning of 17 June was not it. By the time Napoleon got his army on the move, heavy rain began to fall, Wellington successfully parried any attempt by Ney to fix him in place, and Grouchy had lost contact with Blücher.
The Prussians disappeared because instead of retreating east towards their supplies as they were expected, his staff recommended they retreat north in order to maintain contact with Wellington, and the wily Blücher agreed. With no French contact, he had an entire day to reorganize his army. That evening Wellington sent a message that said he planned on defending the ridge near Mont St. Jean if he could be supported by one Prussian corps. If Blücher could not, Wellington planned on withdrawing further. He needn’t worry though.
Blücher replied, “My greatest friend Duke, I will not send just one corps: I will send my entire army.”