The Union General is afraid that the Confederates have 75,000 men and 350 pieces of heavy artillery, when in fact they only have 19,000 men and 18 big guns (information which the Operators hopefully get back to him). This mistake is typical of the blundering that Abraham Lincoln's generals such as George B. McClellan made through most of the American Civil War, and it led to them constantly refusing to attack enemy positions which could win a decisive victory, and giving the Confederates time to regroup and build up their strength for more battles over the same ground. Ulysses S. Grant was given command of the Union Army late in the war, and pressed onto win, but only after 650,000 lives had been lost on both sides. This short seems to be saying that had The Three Stooges been there, the war would have been won swiftly with a minimum of bloodshed.
All Union soldiers are now wearing Union underwear! Think of it!
When they're walking in the river, Major Hyde is walking next to the horse, and both are wearing high-water boots. Just prior, they only show their legs, and its obviously 6 human legs walking in a line.