From the Maryland State Archives, written by Emily Huebner in 2013. Director of this project was Owen Lourie.
The Rain and the Retreat
The morning of August 28, 1776 dawned cold, gray, and rainy. The demoralized American troops were trapped in their Brooklyn entrenchments, an area about three miles around. They were fenced in by the British army to their front and the East River to their back. The two armies were separated by no more than a mile of open ground, and they both kept up a constant peppering of bullets and cannon throughout the day.
U.S. Army - Artillery Retreat from Long Island 1776 (1899)
Approximately five hundred and fifty men were missing the day after the Battle of Long Island. Throughout the morning, survivors of the battle who had evaded capture by the British were straggling back to the American encampment. Major Mordecai Gist and nine other Marylanders returned to the entrenchments that morning, after retreating from the battlefield through the marsh.
The shocking losses of the battle were becoming clear. According to Gist, the killed, wounded, and missing from the First Maryland Regiment added up to about 259 soldiers, and all together, he estimated that the Continental army had suffered a loss of 1,000 men. Most of the missing had been taken prisoner, including Lord Stirling and General Sullivan.
For many Maryland soldiers, the struggle had not ended after the Battle of Long Island, and the men faced new difficulties as prisoners of war. William McMillan, a Marylander who had been captured, wrote that “the Hessians broke the butts of our guns over their Cannons and Robbed us of everything we had. [They] Lit their pipes with our money, caned us into meetings, and gave us nothing to eate for five days, and then [they gave us] biscuits from aboard ships, Blue, moldy, full [of] Bugs & Rotten.” He was later put on a British prison ship and sent to a prisoner of war camp in Halifax, from which he escaped.
The spirits of the Continental army had flagged since the devastating losses at the Battle of Long Island, but their resolve to fight does not seem to have waned. General Washington ordered 1,200 additional troops from Manhattan to march, with considerable pomp, into the entrenchments at Long Island, and the sight of the fresh troops encouraged the weary Americans.
However, the newly arrived troops did little more on Long Island than bolster morale. The following night, the Americans slipped away from Long Island. That night, the 29th, the Marylanders from Smallwood’s battalion were once more ordered to guard the retreat of the American army. The fog and favorable winds during the night and into the morning of the 30th allowed the Americans to escape across the East River to Manhattan without being detected by the British.
The valiant defense by the men who would come to be known as the “Maryland 400″ was already being celebrated the day after the Battle of Long Island. They had “gained immortal honour” for fighting “the enemy, treble in number, in open field, several hours, till at last, surrounded on the side of a small creek, they were obliged to make the best retreat they could.”  With the courage of Marylanders, the Americans had at least secured an honorable defeat.
 Extract of a letter from Head-Quarters, August 28, 1776, American Archives Online, Series 5, Vol. 8, Pg. 28.
 Daniel Blattau, Mordecai Gist, Archives of Maryland (Biographical Series), 2013.
 Jeff Truitt, “Biography of William McMillan”, Archives of Maryland (Biographical Series), 2013.
 Extract of a letter from New-York, August 28, 1776, American Archives Online, Series 5, Vol. 1, Pg. 1194.