Obviously, this won't be the primary focus of the game, but let's be honest: its bound to happen sooner or later, and so I thought it good to toss out a quick primer.
The core of Westerosi tactics is shock. There are infantry and cavalry, with artillery being limited for the most part to siege machinery.
Knights do not rule the battlefield unopposed, but they are still dominant as long as they are well supported. Knights are armored, with wealthier knights armoring their horses as well. Cavalry will tend to occupy the vanguard of an army, and battles often (but not always) begin with a clash of cavalry. Whoever controls the better horse begins at a marked advantage, as they will enjoy greater maneuverability once battle is joined. Command of 'The Van' is seen as the most prestigious post in the army.
That said, cavalry are of limited effect against well disciplined infantry in deep formation (especially pikes, which horses will refuse to charge). They are at their best hitting from the sides or rear of a formation, or running down broken formations. Cavalry troops are composed of noble knights, hedge knights, free lances, mounted men at arms, and squires, with the higher quality troops tending to occupy the front lines of a body of horse. A knight's 'lance' (in the organizational sense) is made up of himself, any free riders he has hired, and his squires. If a knight is unhorsed, his 'lance' is expected to move quickly to his rescue. Bodies of armored cavalry are composed of dozens of mounted 'lances'. This is why, for example- although the Freys could muster over 1,000 cavalrymen- barely 100 of them would be noble knights.
They do not fight as cavalry. What do you think this is, Dorne? Unarmored cavalry are infantrymen who ride to the battlefield, dismount, and fight on foot. In the broken terrain of the Riverlands, the traditional light cavalry roles of scouting, harassment, and raiding are occupied by skilled knights organized into companies of 'Outriders'. Command of the Outriders generally goes to the most canny and experienced knight.
Professional men at arms. It is seen as uncouth for a knight to fight on foot, except in desperation, or being especially courteous in fighting an unhorsed enemy knight. This makes household guards in armor the best footmen a Lord is liable to muster. Heavy infantry tend to be armed with hand weapons and shields, fighting in a tight shield wall formation. Alternatively, some heavy infantrymen carry polearms. Very strong defensive troops, if an army's line of infantry is broken, they are unmade. Command of 'the Line' is the post often given to older knights, who direct the battle from horseback at the rear.
Ironborn warriors, armored in partial maile and carrying shields are also considered heavy infantry, those warriors wealthy enough to afford a sword will often throw spears or axes in the opening moment
In the show, the Lannister spearmen in breastplates are considered Heavy Infantry. In our game, standing House Retainers who are not knights (such as guards, see below) are considered heavy infantry. Unless specified otherwise by their masters, House Guards will be armored in a Leather Jerkin and armed with Sword & Shield.
Lightly armored troops, often filled out by 'calling the banners' (raising peasant levies). Some light infantry such as archers can be well trained and organized troops, but others are there simply to add weight to an army. Men levied from the same town will fight together, under a representative of their Lord. Light Infantry (being amateur soldiers) tend to have difficulty holding formation and fare poorly against enemy cavalry.
Pikemen are often considered light infantry, organized into tight squares to redress this. Many knights look down on light infantry as undisciplined rabble, largely due to the great precision needed- and often lacking- for light formations to operate effectively on the field.
The male peasantry of Hag's Mire are drilled once a week in the handling of a pike. While unpopular, this is considered barely adequate to field functional pikemen.
In this game, all levied smallfolk are considered light infantry. Unless specified otherwise by their lords, Light Infantry are unarmored and armed with either a spear or bludgeon. Common 'upgrades' to levied troops involve equipping them with a shield.
Professional archers tend to use heavy crossbows, while levied peasants will tend to bring their private hunting bows. Longbows are more popular than crossbows in the North, and Iron Islanders tend to neglect archery in their raiding parties (Theon Greyjoy isn't your typical Ironborn). Crossbows are highly regulated weapons, however. It is illegal to own one outside the service of a noble.
Any commander worth his armor will keep a reserve around himself to deploy at whatever point his army is in need of support (or from which to make a rapid escape in case of disaster). Often more cavalry, or bowmen.
In our +combat system, troops in the 'Reserve' stance can only effect, or be effected by the rest of the field through ranged weapons, or until they commit to a attack through a change of stance.
Mercenaries, aka Sellswords:
The only respectable mercenaries are free lances and hedge knights: common born knights and their retinues who serve in exchange for patronage and/or pay when armies gather, and ride with the Lord's knights, often at the forefront of a fight. Free lances, if they prove themselves in battle, will abandon the mercenary lifestyle in a heartbeat if offered a position within a Lord's household.
Less reputable are common sellswords, seen as little better than brigands (a word which derives its meaning from a synonym of 'footman') to be used up as battlefield fodder. Any man not worthy of taking an oath of loyalty to his lord, and selling his services for crass coin is not a man to be trusted, let alone respected in the logic of knightly Westeros.
The standard warship of Westeros is the War Galley, a two masted ship, powered in battle by long banks of oars (typical galleys dip about 100 oars total), with a heavy ram and large artillery piece at the prow. Fortified fighting platforms at the fore and aft of the ship (forecastle and aftcastle) often have arrow slits, and retractable stairs for defense of the ship. A typical naval battle involves firing the artillery shortly before ramming the enemy head on (they aim for flanks, but unless one side greatly outnumber or outmaneuvers the other, it tends to end up being head-on), and fighting a prolonged boarding action. The royal flagship is the King Robert's Hammer, a massive drommond of multiple artillery pieces and over 300 oars. Galleys of all sizes sit tall in the water, making them vulnerable to bad weather, only leaving sight of land in necessity.
In this particular part of the world, however, the Iron Islands Longship (think viking ships) is more common. Small, light and tough, they do not fare well in pitched battle against galleys (boarding much taller ships leaves warriors very vulnerable), a typical rule of thumb being that a single galley can comfortably engage up to a half dozen longships, but they are cheap, fast, and able to row far upriver. A fine raiding vessel, but a poor warship.
Yes, they DO wear armor (chances are, if someone falls into the water, they have already been struck a blow they wished they were wearing armor for) and essentially operate as heavy infantry, described above. Marines are the elite fighting men aboard a ship, but all sailors will grab what weapons are at hand and fight when the ship is boarded, or is boarding.
The War of Conquest (Year 1 A.L.)
The campaign by which the Targaryens united the Seven Kingdoms of Westeros under their rule. although the Targaryen armies were significantly smaller than their enemies, at times on the verge of utter defeat, the Westerosi had no answer for the advantage of three dragons. The Starks and Martells were the only kings among the previous rulers who submitted and therefore survived, while the Arryns, Baratheons, Greyjoys, Lannisters, Tullys, and Tyrells were raised to Lord Paramount status by the victors for their loyalty to the Targaryens.
The Blackfyre Rebellion (195-196 A.L.)
A dispute over the proper succession of the Targaryen dynasty, caused by Aegon IV Targaryen who, on his deathbed, legitimized all of his bastard-born children in the year 184. After a decade of unpopular rule, the legitimately born heir, Daeron II, saw a popular revolt against his rule in favor of his older (formerly bastard) brother Daemon Blackfyre. Although the rebels were finally defeated, the surviving Blackfyres fled beyond the Narrow Sea, where they conspired for generations to return, before dying out in the War of the Ninepenny Kings over fifty years later.
Robert's Rebellion (282-283 A.L.)
Known among Loyalists as the War of the Usurper, this was the uprising which resulted in the overthrow of House Targaryen and the beginning of Baratheon rule over Westeros. A bloody and divisive campaign, ending with a rebel victory following the decisive Battle of the Trident, and the subsequent sack of King's Landing.
Ironborn Invasion (288-289 A.L.)
Called the "Greyjoy Rebellion" in the rest of Westeros, which historians will record as beginning in 289 A.L., this was the war in which Balon Greyjoy named himself King of the Iron Islands, and declared a return to the old ways of reaving and conquest, launching a massive invasion of the mainland. The Ironborn army was driven from the Riverlands after a period of siege and finally defeated on the Iron Islands themselves.
Highly expensive and fully enclosing articulated steel, crafted and fitted to the individual wearer. A single suit is worth more than the total wealth of several towns. Wearing such armor if you are not a noble is considered a crime of theft.
Worn by Heads of House, or their heirs.
Brigadine (aka Plate and Maile)
Helm and a coat of plates worn over a complete suit of maile (coif, hauberk, mittens or gauntlets, and leggings). Favored by noble knights in the Riverlands, whose suits will be markedly more ornate than the example of that barbaric Northman to the left. Squires of such knights will spend many, many hours repairing the odd broken link of maile.
Contrary to what is seen in the show, fighting without a helmet on is not only uncommon, it is stupid.
Breastplate (aka Partial Plate)
A steel open faced helm, gauntlets, and shaped plate encasing the torso and shoulders over the soldier's clothing.
Worn by Sworn Swords in the Riverlands (Riverland houses lack the wealth to outfit common retainers in such harness, unlike the Lannisters).
Maile from head to toe, worn under a cloth surcoat in house livery. A steel helm with a nasal, coif, hauberk, mittens, and leggings. The finest example of this armor (the sort worn by knights beneath brigadine) will see each individual link of maile rivetted closed.
Often worn by nobles from the Iron Islands, or hedge knights in the Riverlands.
A steel cap or maile coif and hauberk worn over a warrior's clothing. Links of maile is such shirts are commonly closed by butting them together, making frequent repairs necessary. An advantage of this harness is that the iron need not be of any quality, not even proper steel. Poorer grade iron maile will tend to rust in spots, quickly.
The most popular harness among raiders of the Iron Islands, who oil the maile regularly to prevent corrosion. On mainland Westeros, the armor is less common, as Lords favor finer harness for themselves, and less expensive, lower maintenance protection for their retainers.
Either hardened leather (the example in the picture to left), or soft leathers reinforced with iron rings. Worn with a cap to protect the head. Low maintenance and relatively inexpensive, such armor is popular among the common soldiers of Westeros.
House retainers and professional sellswords commonly wear this degree of protection.
A long, thick, quilted cloth coat. Usually worn with a steel cap. Troops such as archers or pikemen who are not intended to come into close quarters will often wear this, occasionally reinforced with jackchains. Smallfolk levies won't even get this much.