To land the cannon onto Tybee Island, artillery pieces were taken off transports, set on rafts at high tide, and pitched into the surf near shore. At low tide, manpower alone would drag the guns up the beach. Two hundred and fifty men were required to move a 13-inch mortar along on a sling cart. Later Union amphibious operations would employ "contraband" (escaped slave) labor for much of this work. Along the two-and-a-half mile front, their engineers had to construct almost a mile of corduroy road made of bundles of brushwood to keep the guns from sinking into the swamp. While offloading proceeded day and night according to the tides, Confederate bombardment from Fort Pulaski gunners required all Federal movement into the island limited to night time. After a month of work, 36 mortars, heavy guns and rifled cannon were in position.