Event of the day: Operation Michael

The situation Germany found herself in at the end of 1917 was somewhat mixed. Yes, the defeat of Russia in the East had released a huge number of troops and supplies that could be switched to the Western Front, but the window of opportunity for effective action in the West was rapidly diminishing as the Americans slowly but surely increased their presence in this area. It would only be a matter of time before they were ready to get in on the action in a meaningful way. The pressure was definitely on Germany to go on the offensive and try and win the war before the Allies got any stronger.
With this in mind, Ludendorff got working on his master offensive plan. His idea was simple: to smash the British Army to pieces.
The German army adopted an approach that had succeeded on the Eastern Front, particularly at the Battle of Riga. Their infantry attack would be preceded by an intense barrage concentrated not on the British infantry holding the forward posts, but on the artillery and machine-gun positions, headquarters, telephone exchanges, railways and other important centres of communications. In other words it was a very deep barrage designed to knock out the British ability to respond - but lasting only a few hours before the infantry went in. When the German infantry attacked, they would operate in small groups, specially trained to "infiltrate" - exploiting gaps and moving forward, not worrying about areas that were held up: they would be dealt with by follow-up units. For the British, unused to a discontinuous line and the idea of a deep zone of defended hotspots, such a tactic would spell chaos, uncertainty and disaster. It very nearly worked.
British intelligence had come to the conclusion that a German attack was to be expected, as early as November 1917. It was known to all by March 1918 and only the precise date, time and place was to be determined. Forecasts made by the "E" (Enemy) Group of the British military staff at the Supreme War Council proved to be reasonably accurate but were largely dismissed by GHQ as a result of politics between the two.
At the same time as German strength was growing, the British Army was depleted, having to face up to a manpower crisis and resultant reorganisation, and at a low point of morale after enduring the conditions of Passchendaele and the disappointment after early success at Cambrai.
Operation Michael involved a vast attack along the whole front between the River Oise  and the River Sensée. This area is generally known as "the Somme" sector, although geographically it includes the Cambrésis and the Santerre plateau. The entire area between the St-Quentin/Cambrai front line and the Bapaume/Albert area had been deliberately laid waste by the Germans when they withdrew from that area (in Operation Alberich) in spring 1917. The Bapaume/Albert area had been the site of the Battle of the Somme in 1916. Thus, other than the area west of Albert and on to Amiens, this was in effect one endless area of devastation. The only significant geographical bariers to an advance were the River Somme south of Péronne and the Canal du Nord north of it.

"Main Headquarters
10.3.18
By His Majesty's Orders:
1. The Michael attack will take place on the 21.3.  The first attack on the enemy's lines is fixed for 9.40 a.m.
2. The first great tactical objective of the Crown Prince Rupprecht's Army Group is to cut off the English in the Cambrai salient and reach the line Croisilles (southeast of Arras)-Bapaume-Peronne.  If the attack of the right wing (Seventeenth Army) proceeds favourably, this army is to press on beyond Croisilles.
The further task of this Army Group is to push forward in the general direction of Arras-Albert, keep its left wing on the Somme at Peronne, and intensifying its pressure on the right wing compel the retirement of the English front facing the Sixth Army also, and release further German troops from trench warfare for the general advance.
3. The German Crown Prince's Army Group will first gain the line of the Somme south of the Omignon stream (this flows into the Somme south of Peronne) and the Crozat Canal (west of La Pere).  By pushing on rapidly the Eighteenth Army (right wing of the Crown Prince's Army Group) is to secure the crossing of the Somme and the Canal."

74 German Divisions (roughly 910,000 men) lined up against the British lines. The preliminary bombardment was a hurricane of just five hours where 6,600 guns fired 1,100,000 shells of all descriptions onto the British lines. The bombardment was incredibly accurate, both on the forward lines of the British, but also the reverse areas; smashing communication and transportation infrastructure as well as supplies and reserve camps. Not only did the British lose 7,500 in the barrage, but there was absolute chaos behind the lines.
When the guns fell silent a dense mist had enveloped the entire battlefield allowing the stormtroopers to penetrate deep into enemy territory undetected. The massed infantry followed quickly behind, also covered by the mist, and, despite some heroic defending by the British, over-ran almost all of the British front line areas.
By the end of the first day, the British had no choice but to execute a fighting retreat, they may have inflicted 40,000 odd casualties on the Germans, but they had suffered a similar number themselves and were quite literally, running for their lives.

"The hopes and wishes which had soared beyond Amiens had to be recalled.  Facts must be treated as facts.  Human achievements are never more than patchwork.  Favourable opportunities had been neglected or had not always been exploited with the same energy, even where a splendid goal was beckoning.
We ought to have shouted into the ear of every single man: "Press on to Amiens.  Put in your last ounce.  Perhaps Amiens means decisive victory.  Capture Villers-Bretonneux whatever happens, so that from its heights we can command Amiens with masses of our heavy artillery!"
It was in vain; our strength was exhausted.
The enemy fully realised what the loss of Villers-Bretonneux would mean to him.  He threw against our advancing columns all the troops he could lay hands on.  The French appeared, and with their massed attacks and skilful artillery saved the situation for their Allies and themselves.
With us human nature was urgently voicing its claims.  We had to take breath.  The infantry needed rest and the artillery ammunition.
It was lucky for us that we were able to live to a certain extent on the supplies of the beaten foe; otherwise we should not even have been able to cross the Somme, for the shattered roads in the wide shell-hole area of the first enemy position could only have been made available after days of work.
Even now we did not give up all hope of capturing Villers-Bretonneux.  On April 4, we made another attempt to drive the enemy from the village.  The first reports of the progress of our attack on that day were very promising, but the next day brought a reverse and disillusionment at this point.
Amiens remained in the hands of the enemy, and was subjected to a long-range bombardment which certainly disturbed this traffic artery of our foe but could not cut it.
The "Great Battle" in France was over!"

Surces : http://www.1914-1918.net/bat22.htm
http://www.firstworldwar.com/source/kaiserbattle_hindenburg.htm
http://www.history.com/this-day-in-history/first-stage-of-german-spring-offensive-ends
http://www.scottaddington.com/2012/03/kaiserschlacht-i-operation-michael/