The siege of Dunkirk took place in the Autumn of 1793 when British, Hanoverian, Austrian, and Hesse-Kassel troops under the command of Prince Frederick, Duke of York besieged the fortified French border port of Dunkirk, as part as the Flanders campaign of the French Revolutionary Wars. Following a Coalition defeat at the Battle of Hondshoote they were forced to raise the siege and withdraw northeast.

The decision to besiege Dunkirk was taken not by military commanders, but by the British government, chiefly by William Pitt's closest advisor, Secretary of State for War Henry Dundas. Dundas had considered the possession of Dunkirk as desirable, both as a bargaining chip in negotiations and as a potential British base in Europe. As a military objective towards winning the war, however, it was likely a mistake, as it prevented Prince Frederick, Duke of York from supporting the main Allied thrust further inland, and losing the strategic initiative.

Nevertheless, York followed instructions and through the latter days of August 1793 moved rapidly north-west, leaving the French mystified as to his objective. On 22 August he marched from Veurne (Furnes) to attack Dunkirk with 20,000 British, Austrians and Hessians troops, driving the French advance posts in confusion from the left bank of the Yser River to an entrenched camp at Ghyvelde, capturing 11 guns in the process. The Advance Guard consisting of the Austrian Sztáray Infantry Regiment Nr. 33 and O'Donnell's Freikorps lost 50 men killed and wounded. The commander of the Army of the North, Jean Nicolas Houchard was disgusted when he heard of the flight, writing to his superiors that "The soldiers are good, but the cowardice and crass ignorance of the officers make them learn cowardice, and to fly before the enemy is nothing to them". To protect York's left flank Heinrich Wilhelm von Freytag commanded a corps of 14,500 Hessian and Hanoverian troops which he spread across surrounding villages in a broad military cordon along the Yser to the south of Dunkirk.

On the right Feldmarschall-Leutnant József Alvinczi commanded the Austrian contingent, Lieutenant Generals Ralph Abercromby and Sir William Erskine, 1st Baronet led the British forces, and on the left Lieutenant General Buttlar led the Hessians.

Not only were the French surprised by York's advance, Dunkirk's defences were in a dilapidated condition.The town would most likely have fallen quickly had the promised Royal Navy fleet arrived on time, an English civilian witness wrote to the Public Advertiser that the town would have surrendered outright had it not been for Commissioners arriving from Paris to prevent it.

Meanwhile, in Paris the election of Lazare Carnot and Pierre Louis Prieur to the Committee of Public Safety was to have immediately beneficial consequences for the Republican field armies. Carnot realised that a defeat for Britain before Dunkirk would be a humiliating blow, and consequently, 40,000 men from other sectors were ordered to concentrate to the south of Dunkirk in support of the 5,000 defenders of the town under Joseph Souham. Most of these forces were concentrated near the entrenched camp at Cassel to take part in Carnot's intended flank attack, however on 24 August a column under the command of Jean-Baptiste Jourdan reached Loon, having been diverted from Lille over the head of Houchard by the Représentant en mission, and he was able to reinforce the Dunkirk garrison by 2,500 reinforcements to nearly 8,000, while the remainder occupied Bergues. Burne indicates these reinforcements were the repatriated former garrison of Valenciennes, who by the terms of surrender were supposed to be non-combatant. Jourdan was then transferred to command troops at the Cassel entrenched camp and replaced at Bergues by Leclaire. With the able assistance of his chief of staff, the young Lazare Hoche, Souham, and, later, Jacques Ferrand were able to act vigorously to bolster the demoralized defenders.

On the 24th York's reserve column (Austrian troops plus the flank companies of the British and Hessian regiments) under the Austrian Feldmarschall-Lieutenant Graf Eduard d'Alton took the suburb of Rosenthal and bundled the French back inside the walls of the town. "We suffered very little from their musketry, because they never attempted to dispute the ground with us, but kept firing and retreating; but they no sooner got under cover of their own guns, than they began to open upon us with both grape and round shot, and in our retreat to a convenient cover, we suffered considerably". York reported, "Unfortunately the ardour and gallantry of the troops carried them too far in spite of a peremptory order from me, three times repeated, they pursued the enemy upon the glacis of the place when we had the misfortune to lose many very brave and reliable men by the grapeshot from the town." Fortescue says York lost almost 400 casualties, though the Officer of the Guards gives returns as Austrians 170, British 74 and Hessians 55 killed and wounded. The casualties included d'Alton, who was shot and killed towards the end of the day.

Thereafter York's command began entrenching in a line from Téteghem to the sea. Confidence was high, however York was about to face a number of disappointments. Dundas had omitted to provide York with adequate equipment for a siege, and most importantly no heavy siege artillery. Siege guns had been due to arrive at Nieuport on the 26th, but the only vessels in sight were French gunboats that began bombarding York's right seaward flank with impunity. On 27 August, transports arrived to disembark the gun crews but no guns. On 30 August Admiral John MacBride arrived to coordinate naval operations, but without any fleet.