2. Custer actually did have access to information to how many were in the opposing force; unfortunately, that information was simply wrong.
Contrary to what is commonly reported, Custer had information regarding the strength of the hostiles, which was unfortunately inaccurate, failing to take into account about 800 additional warriors who had fled the reservations and joined the hunting parties, which were the target of the Army expedition. Custer split his command, providing Major Marcus Reno with three companies, Captain Frederick Benteen with another three, and retaining five under his direct command. A final company was left to protect the supply train. Custer was not planning a prolonged action against the village, but a hit-and-run raid to seize hostages.
Following a diversionary attack by Reno, Custer planned to sweep into the village and seize as many of the women and children as possible, meaning that the responding natives would be forced to fire upon their own families within his custody or surrender. It was thus that his insufficient knowledge of the numbers of warriors in the village – a failure of intelligence – that his decision to launch an attack became his fatal error. The Seventh Cavalry was in position about noon, and Custer ordered Reno to attack across the Little Big Horn. Reno quickly realized the size of the encampment and the number of warriors therein, and assumed a defensive position. Under too much pressure to stand and fight Reno was forced back across the river to the elevated bluffs beyond. There he was joined by Benteen’s detachment.