The 1st Division is an infantry division of the British Army that has been formed and disestablished numerous times since 1809 and is still currently active as the 1st (United Kingdom) Division. Lieutenant-General Arthur Wellesley raised the division for service in the Peninsular War, which was part of the Coalition Wars of the Napoleonic Wars. The division was disestablished in 1814 but reformed the following year for service in the War of the Seventh Coalition. It then fought at the Battle of Waterloo, where it repulsed numerous attacks, including the final attack of the day that was launched by the French Imperial Guard. Following the battle, the division marched into France and became part of the Army of Occupation before being disbanded a few years later.

During the mid-to late-19th century, several formations bearing the name 1st Division were formed. According to the current division's official website, three such formations form part of its lineage. The first was formed in 1854 in Ottoman Bulgaria and took part in the Battle of Inkerman and the Siege of Sevastopol as part of the Crimean War; and was disbanded after the end of hostilities. in Africa in 1879, a new division was formed for service in the Anglo-Zulu War but made little impact on the campaign and was again disbanded once fighting ended. The final division to bear the name was formed in 1899 when the Second Boer War broke out. The division was raised in England, sailed to southern Africa, and then fought in most of the major battles to lift the Siege of Kimberley. These battles saw high casualties and were a mix of victories and defeats, and the division's defeat at the Battle of Magersfontein contributed to the political crisis of Black Week. The division saw more success in 1900 but was ultimately disbanded as the British Army reacted to the end of conventional warfare and moved to combat the guerrilla tactics adopted by the Boers.

While all of the earlier formations to bear the name were raised for a particular war, a new, permanent 1st Division was formed in 1902 in the UK. It fought in the First and the Second World Wars, was converted into the 1st Armoured Division in the 1970s, fought in the Gulf War, and was renamed the 1st (United Kingdom) Division in 2014.

Napoleonic Wars Peninsular War

During the French Revolutionary Wars and early in the Napoleonic Wars, the brigade was largest organised formation used by the British Army during campaigns. These consisted of two or more battalions grouped together under the command of a major-general, and suited the small size of the army and the operations it conducted. When needed, larger forces were assembled on an ad hoc basis; these included multiple brigades that were grouped into "lines" or "columns". As the army and its operations grew, it implemented divisions—a single formation of two or more brigades that was usually commanded by a lieutenant-general. The division concept was not new and had been used by other European armies towards the end of the Seven Years' War (1756–1763). On 18 June 1809, Lieutenant-General Arthur Wellesley (later known as the Duke of Wellington), commander of British forces in Spain and Portugal during the Peninsular War, reorganised his force into four divisions—the 1st, the 2nd, the 3rd, and the 4th.

On formation, the division consisted of one brigade of Foot Guards, one brigade of British line infantry, and two brigades of troops from the King's German Legion (KGL). Due to the inclusion of guardsmen, the division was considered a social but not a military elite and was nicknamed "The Gentlemen's Sons". The division of almost 6,000 men first saw action at the Battle of Talavera, where it formed the core of the Anglo-Portuguese Army. A brief action on 27 July 1809 resulted in 188 casualties but the main engagement of the battle took place the following day. Under intense French artillery fire, the 1st was approached by two divisions totalling 15,000 men. The British-German troops had been instructed to hold fire until the French were within close range, to deliver one volley, and then charge. Charles Oman, a historian of the Peninsular War, wrote the division followed these orders and that the leading French ranks "went down in swathes", with casualties amounting to one-third of the French force within ten minutes. The division then recklessly charged after the routed troops and ran straight into the French second line, which rebuked the British and German troops, forcing them to conduct a fighting retreat back to the main Allied position. Redeployed British forces ensured the division was not routed and the line held. By the end of the battle, the 1st had suffered 2,249 casualties.

The next engagement was at the Battle of Bussaco on 27 September 1810, where the 1st Division suffered 141 casualties. This was followed by a general retreat to the Lines of Torres Vedras and skirmishes during the Battle of Sobral. The following year, 828 casualties were suffered at the Battle of Fuentes de Oñoro (3–5 May 1811). In early 1812, the division took part in the Siege of Ciudad Rodrigo and then on 22 July fought in the Battle of Salamanca, where it formed the left wing of the army and defended the village of Arapiles. Back-and-forth fighting took place for control of the village, which resulted in 158 casualties. In September 1812, the division invested the castle at Burgos. Over the next four weeks, it repulsed several French sorties and launched two failed assaults with heavy losses. By the end of the unsuccessful siege, close to 2,000 casualties had been suffered. A general retreat from Burgos followed, during which the commanding officer Edward Paget was captured. His replacement, William Stewart, delayed part of the retreat when he ignored orders issued by Wellington.

In May 1813, a new campaign was launched. After a march north through Portugal, the Allied Army again entered Spain. The following month, the 1st Division fought in a series of battles; San Millan-Osma, Vittoria, and Tolosa, and was present during the opening days of the Siege of San Sebastián in July. In August, the division sent around 400 volunteers to assist in the storming of San Sebastián, with nearly half becoming casualties. The invasion of France followed; the division saw action at the Battle of the Bidassoa in October; it forded the Bidasoa River, pushed back the French defenders, and seized the village of Béhobie with around 160 casualties. Engagements at the Battle of Nivelle in November cost it 193 casualties, and the Battle of the Nive in December brought about a further 289 casualties. After a brief rest, the division forced the Adour in February 1814. Napoleon, Emperor of the French, had abdicated following the 1814 capture of Paris on 31 March while the 1st Division was besieging Bayonne. On 14 April, the French sortied and the division fought in the final battle of the War of the Sixth Coalition, suffering just over 700 casualties. With the war over, the formation was broken up along with the remainder of the army's divisions. The troops marched to Bordeaux, from where they either returned to the UK or were transported to North America to take part in the ongoing War of 1812.

Waterloo campaign

At the end of the fighting, British and Hanoverian troops moved into the Southern Netherlands—previously Austrian Netherlands—as part of an Anglo-Dutch effort to secure the territory while they awaited a political outcome to the war at the Congress of Vienna. On 11 April 1815, after the outbreak of the War of the Seventh Coalition upon Napoleon's return to power and the arrival of Allied reinforcements, the force in the Southern Netherlands was reorganised into divisions. The 1st Division was reformed under Major-General George Cooke and contained four foot-guard battalions, including one that had served with the division during the Peninsular War. The First British Brigade under Major-General Peregrine Maitland contained the 2nd and 3rd Battalions, 1st Regiment of Foot Guards; and the Second British Brigade, under Major-General John Byng, contained the 2nd Battalion of the Coldstream Guards and the 2nd Battalion of the 3rd Regiment of Foot Guards. The division was the only one within Wellington's new army that was composed entirely of British infantry, the other British formations included Hanoverian troops.

The 1st Division's first action of the new war came at the Battle of Quatre Bras. Arriving on the right flank at around 18:30 on 16 June 1815, by which point fighting had been ongoing for several hours, the division launched a counterattack to recapture Bossu Wood that had just been taken. The attack drove out the French but as the British troops advanced beyond the wood, they were repulsed by a second French line and forced back. Fighting continued in and around the woods and included the repulse of a French cavalry attack. Casualties reported for the period 16–17 June amounted to 46 men killed and 508 wounded. Two days later at the Battle of Waterloo, the division formed the right flank of the allied army's front line. Its four battalions were arranged on the reverse slope of the ridge that had been occupied by the Allied army. Their light infantry companies—alongside Hanoverian and Nassau troops—took up an advanced position at Hougomont, a walled farm complex within a wooded area that lay in front of the occupied ridge. The farmhouse and its surrounding area became a vital tactical location.

In the late morning, Napoleon ordered the farm complex and its environs to be captured, beginning the battle. As French troops moved forward, the guns of the 1st Division opened fire and checked several advances. They were not able to completely halt the French, who advanced into the woods and drove the division's infantry back into the farm complex. Sous-Lieutenant Legros, leading a group of French troops, used an axe to breach the gates, allowing a large number of French troops to enter the complex's courtyard. In the following melee, the gates were closed despite the efforts of additional French troops to enter, trapping those within—all of whom were eventually killed in hand-to-hand fighting or were shot by defenders within the buildings. Lieutenant-Colonel James Macdonell and Corporal James Graham were noted for their efforts. As the fighting around the farm continued, Byng's brigade was fully committed to the defence. French troops attempted to encircle Hougomont and attack from the rear. The division's guns again caused the French problems and fresh infantry were moved to check the French moves. An attempt to assault and scale the complex's northern wall and to open the gate from the inside was repulsed. French artillery fire was maintained throughout the day, causing damage to the walls, setting several buildings ablaze, and collapsing the main building's roof. A renewed attack in the late afternoon was also driven off. The final main French assault of the day, which was launched in the evening, was led by skirmishers who engaged with the Hougomont garrison while the main assault pushed past the area to the Allied-held ridge. Following the defeat of the French units, the Allied army conducted a general advance and poured into the Hougomont area to reinforce and clear the position.