The British expedition was much delayed by winter storms, causing the loss of most of the horses and a quantity of ordnance. One transport even found itself back in Cornwall. After a brief time at Savannah to reorganise, Clinton landed on Simmon's Island with 10,000 men, and moved to establish his position on James Island, to the south and west of Charleston. Lincoln remained in Charleston, with 5,500 men, expecting to be reinforced, leaving the British free to advance unhindered towards Charleston. Fort Charleston, on the southern coast of Charleston Harbour, fell on 6 March. However, the British still had to cross the Ashley River, south of Charleston, and find some way to block American escape routes across the Cooper River, east of the city.
The first of these obstacles was easily overcome. A British column crossed the Ashley River at Drayton's Landing, twelve miles above Charleston, without any opposition. This gave them control of the land routes to Charleston. 1 April marked the beginning of the siege-proper when the British forces outside Charleston began to dig siege trenches. However, the loss of much siege equipment at sea meant that the artillery could not prepare for action until the navy could break through to supply them. This happened a week later, and after Clinton offered terms on 10 April the siege guns began their bombardment.
The next day one escape route for the Americans was closed when Tarleton's British Legion defeated an force under Brigadier-General Isaac Huger that was guarding Monck's Corner on the Cooper River. As the siege tightened, American morale plummeted. On 21 April Lincoln made his first surrender offer - he would abandon Charleston if the army could leave intact. This offer was refused.
The siege was again tightened. On 29 April Fort Moultrie on Sullivan's Island guarding the northern entrance to the Harbour fell to a British assault. Tarleton defeated another American force, at Lenud's Ferry on 6 May. Two days later Lincoln made another offer - surrender with full honours of war for the army, with the militia allowed to leave. This too was rejected. Lincoln was now under constant pressure from the civilian population of Charleston to end the siege, and finally on 12 May 1780 the American defenders of Charleston surrendered. Clinton took 5,500 prisoners, including a sizable number of Continentals. A bonus was the capture of four warships of the tiny Continental Navy, trapped in the city.
The immediate aftermath of the capture of Charleston confirmed the most optimistic British expectations. Much of South Carolina rushed to return to British allegiance, with a loyal address from Georgetown and a number of senior local politicians rushing to declare their loyalty. However, Clinton was soon to alienate many who would have been happy with a restoration of British authority by requiring active rather than passive support and the campaign in the Carolinas was eventually to bog down.