The fall of Custer and five of the companies under his command at the Battle of Little Bighorn on June 25, 1876, known by the Sioux Nation as the Battle of Greasy Grass, was as much a failure of reconnaissance and intelligence as of strategy and tactics, and a modern battle between the 7th Cavalry and the Sioux Nation would play out differently.
First and foremost, modern military formations have better intelligence gathering assets. While Gen. George A. Custer labored under the false impression that Sitting Bull, the Lakota leader, had only 800 warriors with him, it's more likely that he had well over 1,000 and possibly as many as 2,500.
When Custer first spotted the signs of the camp on June 25, he wanted to spend time scouting and resting his men before attacking but thought his presence had been detected by Sioux forces and would soon be reported. So, he ordered hasty preparations for an attack.
But modern drones and listening devices would have let him know that the fighters who spotted his men were actually leaving the encampment and not reporting to Sitting Bull. Once Custer knew that and was able to spend time gathering intelligence, he would have learned of the size of the enemy force and at least hesitated to attack with his 647 men without getting reinforcements.
But if he did press the attack anyway, that battle would be most similar to a clash between uneven forces of cavalry and mounted infantry. While Custer's men would likely have enjoyed a technological advantage, the four-to-one numerical advantage of the Lakota, Dakota, Sioux, and Northern Cheyenne forces would have been too much to overcome.
While Custer tried in 1876 to break through to the civilian parts of the camp to force the enemy to either fire in the direction of their loved ones or surrender, a modern Custer would likely try to draw out the enemy forces instead.
To help overcome his shortage of manpower, Custer would likely do this with a careful attack, trying to minimize civilian casualties while inflicting maximum damage on enemy vehicles.
Custer's best chance would likely have been to send anti-armor missile teams into cover and concealment near the Sioux while one or two mechanized infantry companies deployed their Strykers just below the peak on nearby ridge lines.
Then, at a prearranged signal, the Strykers would roar over the ridge and fire TOW missiles at the Sioux vehicles. To keep the technological gap between the U.S. and Sioux forces, we'll say the Sioux predominantly have Bradleys and HMMWVs.
As the Sioux, who were mostly sleeping or resting at the start of the battle, rushed to their vehicles and started moving them to the battlefield, the hidden anti-armor teams could start hitting the vehicles as they passed through chokepoints in the camp and the terrain around it, penning up vehicles.
The mortars embedded in the infantry companies could then start laying it on thick, slamming rounds into the top armor of enemy vehicles and hitting treads and tires with shrapnel to get mobility kills.
But Custer's force of almost 650 troops would find it nearly impossible to keep over 2,000 enemies penned in for long, and the Sioux vehicles would make it into the open sooner or later. Once they did, their superiority in numbers would quickly turn the tide.
Custer could claim a victory at this point, satisfy himself with the large losses already inflicted and conduct an orderly withdrawal while radioing other U.S. government forces to be ready to attack the Sioux forces if they dispersed across the area.
If the Sioux followed him as a large group, he would be able to draw them to a larger government force and wipe them out.
If, instead, he pressed his luck, and continued to fight near the Little Bighorn River, it's likely that the final result would once again be a victory for the Sioux. Once the government anti-tank Strykers and anti-armor teams had expended their missiles, attempts to take the Bradleys out with the Stryker guns would take much longer.
Sitting Bull would be able to get a force assembled, likely by staging it behind one of the hills that dominate the area, and then launch it from behind cover and into the American flank.
Once the American lines were properly disrupted, more and more Sioux vehicles would be able to escape from the camp and launch additional attacks against the beleaguered 7th Cavalry.
While the Sioux would have suffered much heavier losses than in the actual 1876 battle, the end result of a standing battle between the 7th Cavalry and the Sioux nation would always be subject to the huge numbers disparity on the ground.