As a result of the preceding Viking wars, by 1066 the shape of the English military had changed from its earlier form of a Fyrd (militia) that consisted of war bands and hearth troops. First Æleþbald, and then his son Ælfred, had introduced the burghs, fortified towns that were strategically placed, into which the local population could seek refuge during a Viking raid. To defend the walls of the burgh the contemporary Burghal Hidage suggests that it required a man every 1.25 metres (or four men per pole in old terms). To obtain this the local thegns (land holders, what today would be classed as 'gentry') were required to have a residence in the burgh and provide one fighting man per hide of land he held to live in it. The manpower for the burgh was in addition to that required for the Fyrd, which needed to be a mobile force. Ælfred split the Fyrd into three units, one serving in the field, the others at their homes resting and ready to meet any local threat. Service was normally for 40 days. Later this became 2 months.

The result of the above was to place an obligation on the thegns and church to provide armed men in proportion to their holdings, rather than the looser arrangements that had previously existed. Originally the requirement was one fully armed man for every 5 hides of land. The value for a hide is open to interpretation, possibly the nominal amount of land needed to maintain one family. Holding 5 hides was the minimum requirement for thegnhood. Effectively, however, the hide was a financial measure for taxation purposes and towns and their folk were assessed as being worth so many hides, irrespective of the land area involved. Normally the thegn himself was expected to belong to the Fyrd, but he could either nominate another family member, hire a substitute or pay 'scyldscot' to the king to pay for his replacement. The heriot or return of arms to a lord by the estate of a dead thegn was a spear, two swords, shield, byrnie (a protective coat of either ring mail or chain mail), and four horses, two with saddles. This suggests that, in addition to the warrior, he had an armed supporter. The folk from the 5 hides that he represented provided 20 shillings to feed and keep him whilst he was in the field (a rate of pay comparable to a knights fee in post Conquest England). Failure to provide a man meant paying heavy fines and could lead to land confiscation. In addition the king, or his representative (shire reeve or Earl), could call on any free man for either military or auxiliary service. There was a law that states that a ceorl (freeman) who acquired a brynie, helmet and sword, but had no land, could not be a thegn. From this, and examples from heroic poetry of the times, it seems that it was not unusual for ceorls to be fighting in the Fyrd.

Under Knute the Danish Vikings eventually ruled in England. Knute introduced a new element, the Huscarl. Although there had always been 'hearth troops', the Huscarl was more than that. They were in many ways a 'guild' of warriors with their own rules of behaviour and code of conduct. In addition to being fighting men, they also served as royal officials. Service was on an annual basis, with older men being given land for loyal service, as had always been the practice in Germanic society. In addition to the king's Huscarls, the great earls also had their own Huscarls. It is estimated that in 1066 the king had around 3,000 Huscarls and each earl 200.

Generally speaking, the national Fyrd consisted of units of the king, earldoms, shires, hundreds, sokes and stipendiary troops. The shire and hundred men would normally expect to only serve within their own area, though men from the marcher shires bordering Wales and Scotland were expected to serve in those countries as well. The personal forces of the king and the earls served wherever they were needed.

In addition to the above the English had a navy (scip fyrd) that was organised and financed in a way similar to the Fyrd.

The standard strategy was for the king or his earls to ride with their Huscarls to wherever the danger lay and join with the men of the local Fyrd.

The battle tactics in 1066 were the same as had been used for generations. Whilst capable of fighting from horseback, this was normally reserved for hunting down defeated foes after a battle. The standard practice in battle for the English was to fight on foot in a shield wall. Here the armoured thegns and Huscarls would stand in line, often many men deep and close their shields. Part of the Bayeux tapestry shews the Huscarls' shield wall in 'close order', with overlapping shields. This would be ideal for blocking a cavalry attack, however, elsewhere it shews an 'open order' shield wall. Re-enactment groups report that a 'close order' wall drastically reduces the mobility of the shield and prevents it being used to parry an opponent's spear thrust. On this basis 'open order' shield walls would appear to be better for infantry attacks. However, as they are quick to point out, re-enactment groups may not necessarily be using shields in the same way as they were used in Old English times.

A man in a shield wall is open to attack from the man in front and the two men to his left. He is dependent on his comrade on his left to protect him against their thrusts. A man in a shield wall is dependent on both his own shield and the offensive spear thrust of his comrades. For effective use, a shield wall requires its members to stay in line, and thus avoid exposing any man to individual attack on his flanks.

After an exchange of arrows, throwing spears, axes, maces and sling shot the shield walls would clash and spears used to attack the enemy. The dreaded long axe, introduced by the Danes would be used when events allowed a more open shield wall, easily cutting down both men and horses as the Normans found out at the Battle of Hastings at Senlac Ridge. Swords were only used when spear and axe had been broken or lost. If all else failed the shield itself could be used as a weapon, especially if it was of the older round type with an iron boss, though even a blow from than a kite shield can be very painful. In addition to matching shield wall to shield wall, an offensive wedge formation, known as the swine's snout, could be used to try and break the opposing wall. The defence against such a tactic was to withdraw your own shield wall in a V shape where the 'snout' was to strike, and attack the 'snout' on its flanks. To fight effectively in a shield wall requires strong discipline and implicit trust in the men with whom you stand shoulder to shoulder. It also requires constant and dedicated practice to ensure that it holds.

Many who see the Bayeux tapestry, come to the conclusion that much of the Fyrd were little more than armed peasants (though a peasantry in the Continental sense has never existed in England). This misconception comes about for two reasons. Firstly, there is a scene depicting English armed with only shovels and picks being attacked by mounted Normans. The positioning of the illustration indicates it is either shewing a Norman foraging party or the Normans attacking men engaged in building defensive works. The second is the presence in the English force of many men not wearing a byrnie or a helmet. There are two points to be understood here. Firstly contemporary pictures often shew the English fighting or raiding in similar dress, indicating that it was not uncommon to have lightly armed skirmishers in an English army. Secondly, although not armoured, the men still have swords, shields, spear and axes, hardly the sort of thing a peasant would own, let alone know how to use effectively.

The army that only days before had defeated King Harald Hardrada of Norway, acknowledged at the time as Christendom's foremost warrior, was hardly a mob of peasants stiffened by a few Huscarls. Rather it was a balanced fighting force, mixing a heavily armed core with light skirmishers and support troops.

In addition to the surviving Huscarls and thegns of King Harold's and Earl Gryth, the men who fought at Hastings came from Wessex, Kent, East Mercia, East Anglia, and the southern Welsh marches. It is noticeable that the men summoned to gather at the hoar apple tree were from different abbeys (two Abbots died as a result of the battle) and counties than those King Harold took north with him to meet the Norse at Stamford Bridge. This would indicate a sophisticated form of selective summons that ensured fresh troops.

The army that Harald Hardrada brought with him to England and fought at Fulford and Stamford Bridge consisted of men from all over the Norse world. The men from Norway he brought with him had long been engaged in a war with Denmark, and were seasoned men that would have to be considered professionals. The men from the Norse settlements of Ireland would also be in that category, often hiring themselves out as mercenaries. Those from Iceland, Denmark, Sweden, the Faeroes, Orkney, Mann and the sundry isles may well have been opportunists trained to the same level as the English thegns.

The method of warfare and tactics used were the same as those used by the opposing English. This is not surprising considering that the English had originated in Scania, Denmark and the North Sea coast of the Netherlands and Germany. In addition the Viking wars had seen the settlement of many men from the Norse lands, thus reinforcing their commonality.

Whilst William the Bastard, Duke of Normandy had the support of some of his nobles, who brought with them their contingents of armed retainers, much of his army consisted of younger sons and mercenaries from France, Brittany, Flanders and even Germany.

William's army consisted of distinct elements: cavalry, infantry, archers, sappers and support troops.

The French (a more accurate description and one used by both the English and Normans at the time) cavalry were mounted on light horses that were, however, heavier than the ponies used by the English for transport. They wore brynies and conical helmets that were common to them, the English and the Norse. Their primary weapon was the spear. The Bayeux tapestry shews them being used over arm, using the advantage of the height given by being on a horse, and couched as a lance. The tactic of a 'charge' was denied to them at Hastings by the steepness of the hill, and the English shield wall. In addition to spears the cavalry are shewn welding swords, maces and long clubs.

The French infantry at Hastings would have been similarly equipped to the English thegns and huscarls, but without the dreaded long axes. Surprisingly on the tapestry there do not appear to be any light skirmishers other than some of the archers.

The archers William employed appear to have used the common short bow, though it is possible that crossbows were used as well as they were starting to become common in French lands around that time. Some of the archers wore brynies, whilst others were unarmoured. In the last surviving panel of the Bayeux tapestry, where the defeated English are shewn being persued by the French, one archer is mounted.

At that time pitched battles were not anyone's preferred way of waging war, given the individual risks to those involved, especially the leaders. However, the English had leant during their long struggle against the various Viking attacks of the previous 200 odd years that, in order to stop the invader, you have to trap him and force a battle, otherwise he would retreat only to appear somewhere else.

William, on the other hand, was a typical adherent to the contemporary Continental method of warfare with its raids, harrowing and sieges, as expounded in the De Re Militari, a work of the late Roman period by Vegetius. Senlac was the first pitched battle where he commanded, and only the second he had taken part in. The earlier pitched battle William had been in was Val-es-Dunes, which had been primarily a cavalry battle. Whilst William would have been familiar with the shield wall, he was certainly unused to facing an army so well trained in its use as the English, and he would never have had to face the dreaded long axes as welded by the Huscarls. William's lack of experience in overcoming a solid shield wall is shewn in his initial tactic of sending up first infantry, then cavalry against the English. His success did not come until the very end when, in a desperate final fling, he used cavalry, infantry and archers in a combined attack and even then it was a lucky arrow that won him the battle rather than the vaunted cavalry.