The siege of Sluys (or L'Ecluse) of 28 July-25 August 1794 was an early step in the French conquest of the Netherlands in the aftermath of the collapse of the Allied position in Belgium (War of the First Coalition). After their defeat at Fleurus on 26 June the Austrians began to pull out of Belgium, and by late July they were taking up a position on the Meuse, while the British and Dutch were pulling back into the Netherlands. On 18 July the French captured Nieuport, and then moved east to attack Sluys.
In 1794 Sluys (now Sluis, or L'Ecluse in French) was a well fortified town, with modern fortifications (still clearly visible today). It was also the westernmost fortified town in the Netherlands, in an isolated portion of Dutch territory on the southern bank of the Scheldt to the west of Antwerp, connected to the sea by the Zwin channel. The position was also then protected by the island of Cadzand, on the far side of the channel and by a battery of fourteen cannon.
A French force under the command of General Jean Victor Moreau arrived outside Sluys at the end of July. At first the Zwin protected Cadzand, for the French were lacking pontoon bridges or suitable ships, but eventually it fell to an assault in small boats supported by other troops who swam the channel. The British and Dutch made no real effort to lift the siege, and disease was the biggest threat to the French, who suffered 7,000 casualties to the fevers endemic in the area. The city eventually fell on 25 August, removing one threat to the French left wing during the advance into the Netherlands.