unprepared when the French fleet began to arrive off Tybee Island near Savannah and recalled the troops stationed at Beaufort and Sunbury to aid in the city's defense. Captain Moncrief of the Royal Engineers was tasked with constructing fortifications to repulse the invaders. Using 500–800 African-American slaves working up to twelve hours per day, Moncrief constructed an entrenched defensive line, which included redoubts, nearly long, on the plains outside the city. Vessels The British Royal Navy contributed two over-age frigates, and . They landed their guns and most of their men to reinforce the land forces. In addition, the British also deployed the armed brig and the armed ship , the latter from the East Florida navy. There were two galleys, and Thunder, also from East Florida. Lastly, the British armed two merchant vessels, Savannah and Venus. Siege D'Estaing began landing troops below the city on September 12, and began moving in by September 16. Confident of victory, and believing that Maitland's reinforcements would be prevented from reaching Savannah by Lincoln, he offered Prevost the opportunity to surrender. Prevost delayed, asking for 24 hours of truce. Owing to miscommunication about who was responsible for preventing Maitland's movements, the waterways separating South Carolina's Hilton Head Island from the mainland were left unguarded, and Maitland was able to reach Savannah hours before the truce ended. Prevost's response to d'Estaing's offer was a polite refusal, despite the arrival of Lincoln's forces. On 19 September, as Charles-Marie de Trolong du Rumain moved his squadron up the river, he exchanged fire with Comet, Thunder, Savannah, and Venus. The next day the British scuttled Rose, which was leaking badly, just below the town to impede the French vessels from progressing further. They also burnt Savannah and Venus. By scuttling Rose in a narrow part of the channel, the British effectively blocked it. Consequently, the French fleet was unable to assist the American assault. Germaine took up a position to protect the north side of Savannah's defenses. Comet and Thunder had the mission of opposing any attempt by the South Carolinian galleys to bombard the town. Over the next few days, British shore batteries assisted Comet and Thunder in engagements with the two South Carolinian galleys; during one of these, they severely damaged Revenge. The French commander, rejecting the idea of assaulting the British defenses, unloaded cannons from his ships and began a bombardment of the city.