Just finished
Waterloo: The Campaign of 1815 From Elba to Ligny and Quatre Bras Volume I by John Hussey
https://www.amazon.com/Waterloo-Campaign-1815-Ligny-Quatre/dp/1784381969/ref=sr_1_1?dchild=1&keywords=john+hussey&qid=1599093278&sr=8-1This is an excellent operational / strategic dive into the Hundred Days campaign of 1815. The book covers the troop dispositions, message traffic and the difficulty that each of the armies had during the opening of the campaign. The book really shines at the operational level, making me think that this is what it would be like if David Glantz wrote Napoleonic books. The book tends to lean towards the British side, but the Prussians and French are well discussed. The book basks in operational details of supply, logistics, communications and intelligence. You can tell that the author really has a love for the material.
A few things I learned
1) The Saxon contingent of the Prussian Army rebelled in May, 1815, causing significant command and control issues for Blucher. It also meant that Blucher had a significant part of his forces tied up in securing the mutiny.
2) A French division commander (de Bourmont) and five of his staff defected to the Prussians on the night before Ligny. The next day, a French ADC from another division also defected. These should have given the Prussians a bunch of good intelligence on Napoleon's troop dispositions, but the information gained was not exploited.
3) Wellington famously said that Napoleon had "buggered" him by getting the jump on the Allies at the opening of the campaign. The book goes into exhaustive detail proving that this was so. Wellington had indications of French intentions early in the campaign, but inexplicably he did not move until it was almost too late.
4) Poor coordination caused the temporary loss of an entire French corps on June 16th (the day that Ligny and Quatre Bras were fought). Poor intelligence, had Napoleon thinking that Ney only faced 3,000 troops at Quatre Bras. So without consulting Ney, Napoleon pulled an entire corps away from Ney at the height of the Battle of Quatre Bras to reinforce the Ligny battle. The corps (D'Erlon's), got halfway to Ligny when Ney ordered them back. Because of the confused orders, the corps stopped in the middle. They were no good to either Ney or Napoleon. Ney might have won at Quatre Bras if he had had that corps. Then again, Ney was a near crazed wild-man so probably would have lost Quatre Bras anyway.
5) Support for Napoleon in France was far from universal. There was a significant rebellion just at the cusp of being put down when the campaign opened. Napoleon had to send about 10,000 troops to put it down, at a time when he needed every available musket in Belgium.
Anyway, I recommend this book for anyone wanting a deep dive into the opening of the campaign. As in the title, Volume one only goes through Ligny and Quatre Bras. But I definitely have Vol. II in my reading list.