William the Conqueror and the Principles of War

Written by Sir Kirk fitzDavid. Originally published in the Online Bird of Prey, Volume 5, Third Quarter 2002

Warfare in medieval Western Europe appears, at first glance, to have been conducted by amateurs.  When compared to the Romans who came before, and the Swiss and English armies which developed in the 14th century, medieval armies often seem like undisciplined mobs stumbling around the countryside as often missing as finding their opponents.   Campaigns were usually made up of massive raids or long sieges, with little permanent result.  Tactically,  this picture is not completely wrong since most armies were not well disciplined, inflexible mass formations were the rule, and cavalry was often a “fire and forget” weapon.  Strategically, few commanders seemed to understand and use what we term the “principles of war” today.  Perhaps the most successful commander in medieval Europe, however, demonstrated an intimate familiarity with the principles of war and used them successfully through most of his many campaigns.  This commander was William the Conqueror.

As they are used today, principles of war are enduring concepts such as surprise, offensive, maneuver, supply, and mass.  The list varies from person to person and country to country, but includes tools which a commander can use to achieve victory, and factors which he must take into account to prevent defeat.  They are not a step-by-step recipe for war, but when used together they enhance each other’s effects.  For example, the principle of mass is generally defined as grouping a large enough force together to meet your objective.  Maneuver, of course, is moving your forces in relation to the enemy.  By combining the two, massing your force and moving to a weak point in the enemy’s forces, you might be able to attack and win.  An attack without massing enough forces would be defeated, and attacking where the enemy is strongest doesn’t often work, either.

William the Conqueror used many of the principles of war to great effect.  He achieve particular success with the principles of objective, offensive, mass, economy of force, maneuver, surprise, security, and supply.  The objective is aim of the campaign, what you hope to achieve.  To be on the offensive is to take and hold the initiative, and make the enemy react to your moves.  You call the shots, not him.  Economy of force is the opposite side of the coin from mass.  It means not wasting your strength in areas you don’t need it.  Surprise is attacking where your enemy is not ready and cannot react effectively in time to prevent your move.  Security is preserving your freedom of action.  The best example of this is to prevent the enemy from surprising you.  Supply (or logistics) is providing your forces with the materials they need to win–food, fodder for animals, arms, armor, etc.  Finally, William used one more technique which we don’t consider a principle of war, but he probably thought of as equivalent to modern principles.  This was terror or intimidation, and he turned to it when he thought it would serve his purpose better than other methods.

William conducted campaigns throughout his adult life, from the time he secured his duchy at the battle of Val-es-Dunes in 1047 until his death from injuries he suffered at the sack of Mantes forty years later.  Three of his campaigns illustrate his strategic mastery of the principles of war.  He used offensive, maneuver, surprise, and terror to defeat Geoffrey of Anjou’s invasion of Normandy in one of his earliest campaigns in 1051.  William defeated the most serious rebellion of his reign in England in 1069-70 by again using maneuver, mass, economy of force, and terror to beat one rebel group after another.  And in his greatest campaign, William was able to mass his forces, keep them supplied, and secure Normandy behind him in order to launch his invasion of England in 1066.

William faced the first invasion of Normandy in 1051.  The county of Maine, on Normandy’s southern border, was taken over by Geoffrey, Count of Anjou, when the old count died.  After moving into Maine, Geoffrey continued north and took the fortresses of Domfront and Alencon on the Maine-Normandy border.  In early fall, William gathered his forces to counterattack.  He took the offensive, moving into the area between the fortresses, and attacked Geoffrey’s army.   He drove off Geoffrey after some hard fighting, giving him the freedom to besiege Domfront.

The duke was not content to conduct a long siege.  Leaving part of his force at Domfront, William marched the 35 miles to Alencon in one night.  This surprised the garrison, and William took the town by assault.  The defenders had apparently mocked William by waving hides from the walls (William’s grandfather was a tanner).  He took his revenge on them by cutting off the hands of the captured garrison. He returned to the siege of Domfront, and his cruelty so intimidated the defenders that they surrendered with his promise of good treatment.

William had used the principles of offensive, maneuver, surprise, and finally terror in sequence to conduct his campaign.  He regained the initiative by taking the offensive against Count Geoffrey, and driving him from the field.  This victory gave the duke the freedom to maneuver, first besieging Domfront and making his sudden move against Alencon.  His sudden attack surprised the defenders, and he overpowered them without a siege.  His cruelty intimidated the last opposition and finished the campaign.

 In 1069-70, a rebellion and invasion of England forced William to conduct an even more remarkable war of offensive and maneuver.  He had already put down some small, uncoordinated rebellions in England after the conquest.  In the summer of 1069, the sons of Sweyn Estrithson, King of Denmark, raided the English coast from Kent to the Humber.  The Viking army was nearly the size of Harald Hardraada’s, and came ashore near York as Harald’s had three years before.  This sparked a general rising in Yorkshire, and English rebels joined with the Vikings to attack and wipe out the Norman garrison in York.  The revolt rapidly spread, to Chester in the west and Dorset and Somerset in the southwest.  The Scots provided support in the north, and the Welsh aided the western rebels.  The Danes spread out and moved south from York, and were welcomed by the English.  The Normans had lost control of almost all of northern England.

King William reacted quickly.  He gathered an army and moved north toward the Danish force, and the Vikings pulled back north over the Humber.  Leaving enough troops behind to keep the rebellion from spreading south again, William turned west to deal with the rebellion around Chester.  He suppressed the rebellion there, and sent troops south to deal with Dorset and Somerset.  By this time the Danes were moving again, and were heading for York again.  William returned to Yorkshire, burning the land that had welcomed the Vikings.  When he arrived at Christmas, William decided to suppress the rebellion once and for all by destroying all means of livelihood.  He killed all the adult men he could find, and destroyed all the livestock and farming implements.  The devastation was so great that the damage was readily evident in the Domesday Book, and the area did not completely recover for 70 years.

William bribed the Danes to leave by letting them keep the booty they had gathered so far, and allowing them to stay the winter before returning to Denmark.  This let him return to Chester, where the rebellion had resumed when he left.  William had to march through a terrible storm in the dead of winter, but he and his army arrived in time to disperse the rebels once and for all without serious fighting.

Offensive, maneuver, mass, economy of force, and finally terror were William’s tools in crushing the rebellion.  From his first moves against the rebellion, William kept constantly on the offensive.  He never let the disjointed parts of the rebellion unite, and maneuvered rapidly against each in turn until all the outbreaks were crushed.  William first massed his forces to deal with the most serious threat, the Viking army.  He then carefully split off detachments, either to hold the line in the north or to deal with the southern rebellion.  Finally, to end the repeated revolts, he again used the option of terror by devastating the countryside and destroying the ability of his people to live, let alone rebel.  His tactic of cruelty was entirely deliberate, because William had demonstrated his control over his troops in many other wars.  He had prevented the sacking of cities after sieges such as at Exeter in 1068 and Domfront above, and had put down the earlier English rebellions without much destruction.  But clearly he was out to make an example of Yorkshire and to deter any future rebellion against him.

In his most successful campaign, William invaded England and defeated King Harold.  To do this, though, he had to demonstrate his mastery of the principles of mass, supply, and security.  William had to assemble and transport a very large army for the time.  He needed to take all the Norman troops he could, and hire mercenaries to give him the numbers he needed to defeat the large English army.  He had to keep all these soldiers fed, as well as building the ships to take them across the English Channel.  William also had to worry about the security of Normandy while he was gone.  He had to make sure he wouldn’t lose his duchy to a sudden attack while most of the troops were gone.

At the end of Edward the Confessor’s reign, England had one of the largest armies in Europe.  Several thousand huscarls were always available.  The select fyrd acted as trained reserve, and could be quickly mobilized to form a large, infantry-based army.  William’s army needed to be nearly as large as Harold’s to gain a victory.  Much of his strength was in cavalry, and he needed to build hundreds of ships just to transport his 2,500 or so horses.  To get as many men as possible, William hired all the mercenaries he could, either paying up front or promising land in England.  He also pressed his Norman vassals hard to bring all the troops they could.  William managed to gather a force of about 10,000 soldiers and sailors, with at least 700 ships.

While gathering his force, William faced two problems.  How could he supply his troops, and how could he keep Normandy from being attacked while he was gone?  The second problem was more complicated, and William started on it almost as soon as he decided to invade England.  In the previous 20 years, William had fought against France, Anjou, and Brittany at one time or another.  He was ringed by potential enemies.  He decided to conduct a diplomatic campaign to both justify his claim to the English throne and to prevent attack on Normandy.  William first got the Pope to declare his invasion of England a crusade.  This made any attack against Normandy an attack against the Church.  William also sent ambassadors to King Sweyn of Denmark, Philip I of France, and Henry IV, the Holy Roman Emperor.  None of them promised William aide, but they all promised to help if Normandy were invaded.  Finally, William left a few of his most trusted and powerful vassals behind to help his wife rule the duchy.

William achieved his greatest success in his handling of the supply problem.  Armies of the time carried no more than30-60 days of supplies when they gathered for a campaign.  After that ran out, the armies either broke up and went home, or plundered the countryside for food.  William began building his fleet in the spring, and did not finish until the end of July.  Then, for six straight weeks, he waited for favorable winds in order to sail.  He needed to keep the army concentrated so they could board the ships as soon as a good wind arose.  But he also couldn’t let it forage in the countryside, or his vassals would desert so they could defend their homes and land.  He had to buy mountains of supplies to keep the army fed, and use his powerful personality and persuasive arguments to keep his troops from plundering.  Without this success, the invasion would never have been launched.

All this planning and preparation was required just to get the invasion underway.  Compared to the personality conflicts, supply problems, and defections that plagued the First Crusade only thirty years later, this must have been a model of an efficient, well-organized army.

William the Conqueror demonstrated his mastery of the principles of war throughout his adult life.  His campaign against Geoffrey of Anjou combined the offensive, maneuver, surprise, and finally terror in sequence to drive the Angevin forces from his territory.  He again used maneuver, backed up by mass, economy of force, and terror, to defeat a rebellion which had taken nearly half of England from his control.  And his careful planning and preparation enabled William to mass his troops for the invasion of England, keep them supplied, and secure Normandy while he was away.


William the Conqueror, by David C. Douglas.   This biography of William is widely available, and is the most comprehensive book I’ve found on him.  Covers the politics and military matters very well, though the battles aren’t as detailed as they could be.  William’s ruling methods and relations with the Church are given particular attention.

1066:  Year of Destiny, by Terence Wise.  A much better book for getting the flavor of the times.  Covers the Vikings and the English as well as the Normans, with plenty of good maps and pictures.  Incorporates a great deal of recent (after 1950) archeological information.  Wise has the unconventional opinion that the English army, and in particular the huscarls, fought from horseback much of the time, including at Stamford Bridge (but not Hastings).  Also covers events in England up to 1070

Invasion:  1066, by Robert Furneax.  A somewhat dated book, focusing mostly upon Hastings. Fills some gaps in the other two.

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