There are bad guard details, horrible guard details, and then guard details where you and the bulk of your regiment are ordered to guard caves filled with bat shit.
Gunpowder is made up mostly of saltpeter, a chemical powder generally mined from deposits on cave walls or extracted from urine and bat guano. When the South found itself under naval blockade early in the war, it had to find a way to make many of its necessities.
To make the saltpeter necessary to manufacture gunpowder, the Confederacy turned to large bat guano deposits near Austin, Texas. One deposit area was later estimated to contain at least one-thousand tons of guano.
The Confederate government ordered the deposits guarded to ensure wartime production was secured, but it’s unclear how much saltpeter was actually manufactured before the end of the war. The caves were later put back into production during World War I.
Modern ammunition uses cleaner-burning propellants, but the nitrates in guano are still valuable for fertilizers. The descendants of the bats that provided the guano are now famous in Austin. Spectators line up on bridges to watch the bats depart for their nightly feeding.