The Spanish Invasion of Portugal and the Defense of Britain's Oldest Ally (1762)

As Britain and Spain entered open war in 1762, the most immediate threat was a Spanish invasion of Portugal, which had remained neutral for most of the conflict despite its historic alliance with Britain. Encouraged by France, Spain sought to open a new front that would force Britain to divert troops away from its campaigns against France, particularly in North America and the Caribbean.

Spain’s Strategy – Attacking Portugal Instead of Gibraltar

Although Spain had long sought the capture of Gibraltar, the heavily fortified British stronghold presented a formidable challenge. Instead, France persuaded Spain to invade Portugal, believing its long but rugged borderwas vulnerable and easy to overrun. By capturing key Portuguese cities, Spain hoped to force Lisbon to break its alliance with Britain and potentially gain strategic leverage in the broader war.

Britain Responds to the Threat

Recognizing the danger, Britain moved swiftly to reinforce Portugal, dispatching supplies, military officers, and troops to help organize its defense. The original Spanish plan was to capture Almeida, then advance toward the Alentejo and Lisbon, but the strategy shifted to Porto, aiming to strike directly at British trade interests.

The Spanish Advance and British-Portuguese Resistance

In the spring of 1762, under the command of the Marquis of Sarria, Spanish troops crossed from Galicia into northern Portugal, quickly capturing several towns. However, their advance on Porto was slow and disorganized, hampered by:

• Difficult terrain
• Heavy flooding of the River Esla
• Supply and coordination problems

By May 9, Spanish forces invested and captured the key border fortress of Almeida, dealing a serious blow to Portuguese defenses.

The British-Portuguese Counterattack

Britain responded by dispatching 8,000 troops to Portugal:

• 6,000 troops arrived from Belle Île, under Lord Loudoun
• 2,000 more troops came from Ireland

As reinforcements landed, a British-Portuguese counterattack, led by John Burgoyne, struck back at the Spanish, capturing the town of Valencia de Alcántara. This bold maneuver disrupted Spanish supply lines and demonstrated that Portugal’s defenses were stronger than anticipated.

French Intervention and the Bourbon Retreat

France, eager to support its Spanish ally, sent reinforcements, but these forces, like their Spanish counterparts, suffered high rates of attrition due to:

• Disease
• Desertion
• Logistical failures

By November 1762, with supply and communication lines stretched thin, the Bourbon allies recognized the futility of their campaign. Facing increasing resistance and unable to secure a decisive victory, they withdrew from Portugal and sued for peace.

A War Without Major Battles

Despite the large number of troops involved, the campaign saw no major battles. Instead, the Spanish invasion was characterized by logistical failures, difficult terrain, and an underestimation of British-Portuguese resistance. In the end, Britain's swift military response, Portugal’s resilience, and the Spanish-French inability to sustain the campaign ensured that Portugal remained unconquered, reaffirming its place as Britain’s oldest ally.

The Spanish Invasion of Trás-os-Montes and the Rising Popular Revolt (April–May 1762)

On April 30, 1762, a Spanish force crossed into Portugal through the province of Trás-os-Montes, marking the first incursion of the Franco-Spanish invasion during the Seven Years’ War. To justify their actions, the Spaniards posted a proclamation titled "Reasons for Entering Portugal," in which they claimed they were not invaders, but liberators, coming to free the Portuguese people from the "heavy shackles of England," which they denounced as the "tyrant of the seas."

However, these words were soon betrayed by actions, as Spain’s logistical failures led to widespread resentment and armed resistance among the Portuguese population.

The Main Invasion Begins (May 5, 1762)

On May 5, 1762, a major Spanish force of 22,000 men, led by the Marquis of Sarria, launched the full-scale invasion of Portugal. The response from Lisbon was immediate:

• On May 18, Portugal officially declared war on Spain and France, making its neutrality a thing of the past.
• British reinforcements were not yet in place, and the Portuguese army was still in disarray, forcing the defenders to rely on fortresses and guerrilla resistance.

The Spanish March Through Trás-os-Montes

The first target was the fortress of Miranda, the only well-fortified and provisioned stronghold in the province. However, fate turned against the defenders:

• On May 6, a catastrophic accidental explosion in the fortress's powder magazine—containing twenty tons of gunpowder—killed 400 Portuguese soldiers and opened two massive breaches in the walls.
• With no alternative, Miranda surrendered on May 9, giving the Spaniards their first victory.

With no remaining strongholds and no organized troops in Trás-os-Montes, the Spanish march became effortless:

• Bragança fell on May 12
• Chaves was occupied on May 21
• Torre de Moncorvo surrendered on May 23

These towns were undefended and surrendered without a single shot fired. Powder and provisions were nonexistent, and the Spanish general reportedly mocked Portugal’s lack of soldiers, joking:

"I cannot discover where these insects are."

Spanish Overconfidence and Logistical Failures

At first, the Spanish maintained good relations with the local population, even paying double for food and other provisions. Madrid had miscalculated, assuming that Portugal would quickly submit and that the mere presence of a powerful invading force would be enough to force surrender.

However, this assumption would prove to be a fatal error, for two critical reasons:

1. The Spanish Army Had Entered Portugal Without Enough Provisions

   • Confident that Portugal would capitulate quickly, the Spanish had not brought adequate food and supplies.
   • The campaign became unsustainable, as they were unable to feed their troops.

2. The Spanish Assumed That Portugal Could Sustain Their Army

   • Spanish planners assumed local populations would be able to provide sufficient food and resources.
   • When this proved an illusion, Spanish commanders resorted to forced requisitions, taking what they needed by force.

The Spark of Popular Revolt – "War for Food Feeding War"

The moment the Spanish began seizing food and supplies from the local populations, the relationship between the invaders and the Portuguese civilians collapsed.

• Peasants began resisting Spanish foraging parties, sometimes using improvised weapons.
• Local militias, supported by Portuguese irregulars, started attacking supply convoys, cutting off food to the Spanish troops.
• The initial goodwill was replaced by open hostility, turning Trás-os-Montes into a battleground of guerrilla warfare.

This "war for food feeding war" transformed the campaign. Instead of a swift and easy conquest, the Spanish found themselves bogged down, suffering from food shortages, harassment, and an increasingly organized resistance.

Strategic Consequences

The Spanish offensive, which had begun with little resistance, now faced a logistical nightmare:

• Troops were starving, forcing them to retreat to secure supply lines rather than advancing deeper into Portugal.
• The Portuguese irregulars and Ordenanças were gaining momentum, exploiting the terrain and Spanish weaknesses.
• The Bourbon plan for a quick Portuguese surrender unraveled, as the Portuguese populace refused to accept the invaders as "liberators".

While the Spanish and French still had a numerical advantage, their logistical failures and growing Portuguese resistance would ultimately doom the invasion. By the end of 1762, the Bourbon allies would be forced to withdraw, marking a humiliating failure in their attempt to bring Portugal into the Family Compact by force.

The Collapse of the Spanish Invasion – A Retreat Amidst Carnage (June 1762)

By June 1762, the Spanish invasion of Portugal had completely unraveled. Not only had the Spanish failed to achieve their main military objective—capturing Oporto—but their forces were now suffering catastrophic losses from disease, famine, and relentless guerrilla warfare.

A contemporary account describes the nightmare unfolding in Trás-os-Montes, stating that the stench of unburied Spanish corpses filled the mountains, as local peasants, motivated by hatred, refused to bury the dead. The scene bore striking similarities to the fate of Napoleonic soldiers decades later, who also met fierce Portuguese resistanceand suffered immense casualties.

Catastrophe in the Occupied Cities

Even inside Spanish-occupied cities, the invaders found no refuge. In Chaves, where 500 Spanish miqueletes had taken control on May 21, 1762, only 18 remained alive by the end of June—a stunning testament to the effectiveness of Portuguese irregular warfare.

Spanish Casualties and Desertions

According to the Spanish military historian José Luis Terrón Ponce, total Spanish losses during the first invasion of Portugal—from guerrilla attacks, disease, and desertion—exceeded 8,000 men.

Even more damning, General Charles-François Dumouriez, writing in 1766, estimated the figure at 10,000 casualties and explicitly recommended that Spain never again attempt an invasion through Trás-os-Montes, warning of the region's hostile terrain and population.

Final Collapse and Spanish Retreat (End of June 1762)

By the end of June, the Spanish position was untenable:

• The invasion’s primary objective—Oporto—remained out of reach.
• The Spanish army was decimated by starvation, disease, and guerrilla ambushes.
• Guerrilla forces had successfully cut off food supplies, worsening famine among Spanish troops.
• Portuguese regular forces, advancing from Lamego, threatened to cut the Spanish army in two—one force trying to cross to the southern bank of the Douro, the other still attempting to reach Oporto via the mountains.

Facing total collapse, the Spanish high command ordered a full retreat toward Spain, abandoning all their conquests except the city of Chaves, which they held on the frontier.

Conclusion: A Humiliating Defeat for Spain

The failure of the 1762 Spanish invasion of Portugal was one of the most disastrous campaigns in Spanish military history. Spain had underestimated Portuguese resistance, assuming that a swift invasion would force Lisbon to surrender. Instead, the Spanish lost thousands of men, saw their army harassed at every turn, and failed to achieve any meaningful strategic objectives.

By the end of June, the Spanish were not just retreating—they were fleeing for survival, marking the complete failure of their first attempt to bring Portugal into the Bourbon Family Compact by force.

British Reinforcements Arrive and the Reorganization of the Portuguese Army (1762)

As the Spanish invasion of Portugal collapsed, British reinforcements arrived, strengthening Portugal’s ability to counterattack and expel the remaining invaders.

British Expeditionary Force Lands in Portugal

Britain, committed to defending its oldest ally, dispatched a significant military force to Lisbon in two waves:

• May 1762: The advance force, commanded by Major General George Townshend, included:

  • The 83rd and 91st Regiments of Infantry
  • The major portion of the 16th Light Dragoons

• July 1762: The main force, arriving from Belle-Isle, consisted of:

  • The 3rd, 67th, 75th, and 85th Regiments of Foot
  • Two companies of the Royal Artillery

The total strength of the British force was 7,104 officers and men, a precise figure known from official records.

In addition to troops, Britain also provided:

• Provisions and munitions
• A loan of £200,000 to support the Portuguese war effort

Friction Between the Allies

Despite their common enemy, tensions arose between the British and Portuguese forces due to:

• Language barriers that complicated orders and coordination
• Religious differences, as Portugal remained strongly Catholic while Britain was Protestant
• Salary discrepancies, as British officers were paid double their Portuguese counterparts, maintaining their higher pay from British service

Lippe’s Leadership: Rebuilding the Portuguese Army

To ensure military effectiveness, Count Wilhelm von Schaumburg-Lippe, the Allied supreme commander, took decisive action to reform and integrate the Portuguese army with the newly arrived British forces.

• Out of 40,000 Portuguese soldiers, Lippe selected only 7,000–8,000 as fit for service, dismissing the rest as unfit for war.
• This restructured army, combined with British troops, formed a professional Allied force of approximately 15,000 regular soldiers (about half Portuguese, half British).

Portuguese Militia and Defense Strategy

• Militia and Ordenanças (second- and third-line troops), numbering around 25,000 men, were assigned to garrison fortresses rather than field operations.
• A small force of regular Portuguese troops remained in northern Portugal, keeping watch on Spanish forces in Galicia.

Facing Overwhelming Odds

The 15,000-strong Anglo-Portuguese army faced a formidable enemy, as Spain and France had gathered an invasion force of 42,000 men:

• 30,000 Spaniards, led by the Count of Aranda
• 10,000–12,000 French troops, commanded by Prince de Beauvau

Despite being vastly outnumbered, Lippe would successfully integrate the British and Portuguese armies, rebuild discipline and organization, and lead a defensive campaign that would ultimately secure Portugal’s survival and victory.

His strategic leadership and effective use of limited forces ensured that Spain and France would fail in their objectives, marking one of the most remarkable defensive victories of the Seven Years’ War.

A National Rebellion and the Collapse of the Spanish Invasion (June 1762)

By mid-1762, Madrid remained confident that Oporto would soon fall, and Spanish officials expected an imminent victory in Portugal. However, rather than submission, the invading forces were suddenly confronted with an escalating national rebellion—a popular uprising that would prove far more devastating than the Portuguese regular army.

Portuguese Resistance Turns into National Revolt

The spread of the rebellion throughout Trás-os-Montes and Minho changed the character of the war:

• Francisco Sarmento, the governor of Trás-os-Montes, issued a declaration ordering the population to resist the Spanish invasion or be branded as traitors.
• Entire villages were abandoned, leaving the Spanish troops with no food, guides, or laborers to help build roads and supply routes.
• Portuguese militias and Ordenanças, along with bands of armed civilians, ambushed the invaders, taking advantage of the rugged terrain.
• The Spanish army faced high casualties, suffering from disease, starvation, and relentless guerrilla attacks.

Eyewitness Accounts of Spanish Struggles

British newspapers published reports detailing the Spanish difficulties in the field. According to a British source from Almeida, dated June 12, 1762:

“The Enemy [Spaniards], to the number of eight thousand, has entered the frontier… several parties had rallied forth from the camp and had pillaged the villages upon that frontier, and had not even spared the churches; but these parties had been driven back by the Portuguese militia, who had killed and taken prisoners upwards of two hundred Spaniards.”

Similarly, from Minho, June 20, 1762:

“Those [Spaniards] who retired from Villa Real and Mirandela towards Miranda were attacked upon their march by the militia… who killed some of the Spaniards and took twenty odd prisoners… We have advice of the 22nd [June] that a convoy of sixty mules, laden with provisions, had been taken from the enemy about two leagues from Chaves.”
(Martin, Benjamin – Miscellaneous Correspondence, vol. IV, London, 1764, p. 904.)

A Crisis of Attrition: Disease, Starvation, and Guerrilla Warfare

As Spanish forces struggled to maintain control, the rebellion intensified, with severe consequences for the invading army:

• According to a French contemporary source, more than 4,000 Spanish soldiers perished in the hospitals of Braganza—killed by wounds, disease, and starvation.
• Convoys transporting food from Spain were intercepted and destroyed by the Portuguese militia, cutting off critical supplies.
• Small Spanish detachments, assigned to protect food foraging missions, were frequently ambushed and annihilated by local fighters.

Even King Charles III of Spain, in his formal declaration of war against Portugal on June 15, 1762, complained about the "treacherous" Portuguese peasants, who, according to his government, had been conducted by undercover officers to kill Spanish detachments in surprise attacks.

The Spanish Army Falls Apart

Facing a growing national rebellion, the Spanish army was forced to split its forces to:

1. Defend occupied towns from guerrilla attacks.
2. Find food, since Portuguese peasants refused to supply them.
3. Escort convoys bringing provisions from Spain, which made them vulnerable to Portuguese ambushes.

Without a quick victory at Oporto, starvation and attrition would render the Spanish position untenable. The invasion was no longer a military operation—it had become a desperate fight for survival.

Conclusion: The Invasion on the Brink of Collapse

By June 1762, Spain and France realized that their strategy had failed. Rather than welcoming them as liberators, the Portuguese people had turned the countryside into a battlefield.

With food shortages, heavy losses, disease, and an escalating rebellion, the Spanish invasion of Portugal was unraveling—and unless they could secure a decisive victory soon, they would be forced into a humiliating withdrawal.