them. The first wave of 500 men aboard Granite City which steamed as close behind Clifton as possible but out of range of the fort's guns, were to land in the open space adjacent to and downstream of the fort. This was a flat, often muddy area already cleared of brush by the Confederate garrison as a clear field of fire for the canister and grape of the fort's artillery. The U.S. Army's invasion plan, therefore, absolutely required that the Confederate guns be silenced before any troops were debarked. This engagement was to be the largest amphibious assault on enemy territory in the history of the U.S. military up to that date. Leon Smith, who was at Beaumont, Texas, immediately ordered all Confederate troops in Beaumont, some eighty men, aboard the steamer Roebuck and sent them down the river to reinforce Fort Griffin. Smith and a Captain Good rode to the fort on horseback, reaching the fort some three hours before the steamer, arriving just as the Union gunboats and Sachem came within range, and assisted in the defense of the fort. Dowling's well practiced Irish-Texan artillerymen, whose chosen and officially approved unit name was "Jefferson Davis Guards", had placed range-stakes in the two narrow and shallow (5-to-7 feet or 1.5-to-2.1 m) river channels. These were the "Texas channel" near the southwest shore and the "Louisiana channel" against the Louisiana shore. The white-painted stakes were for determining accurate range of the fort's guns: six old smooth-bore cannon. Each "Davis Guards" gun crew during gunnery practice thereby worked to predetermine the approximate charge (amount of gunpowder) needed for each type projectile available for their specific gun (ball, canister, or grapeshot); and which specific guns, charges, and loads had the best potential to hit each range-stake. Crocker's squadron had no local river pilots, only general knowledge of the river's channels, no assurance of locations of the constantly varying depths especially of large oyster-shell "reefs" or "banks" between the river's two channels. Regarding this battle no mention is found in official U.S. Navy reports of whether Union sailors were making observations and taking depth soundings from the gunboats' now dangerous top decks, while the Confederate cannon shots pounded and shook their ships. The few maps to which they had access were old and outdated or could not account for recent changes in river-bottom conditions. On Captain Crocker's signal the Sachem, followed by Arizona,