If someone is bleeding badly, they have about thirty-six minutes. A JAMA study of combat injuries in Afghanistan found that nearly anyone who receives blood inside that window survives, and after it the odds fall away fast.
Which makes it a logistics problem wearing a medical coat. Whole blood keeps thirty-five days, refrigerated, and the cold chain has to reach wherever the bleeding is.
February 2007, near Karmah. A casualty evacuation helicopter, call sign Morphine 1-2, flew through insurgent-held territory in broad daylight — something crews never do — because it was carrying blood and the blood had somewhere to be. A missile locked on. The pilot fought the burning aircraft for fifty-eight seconds. All seven crew were killed.
DARPA now wants freeze-dried blood by 2029: a powder a medic carries in a backpack and rehydrates in the field. No refrigeration, no cold chain, no daylight run through hostile ground.
What that engineering is really aimed at is removing the reason anyone had to make that flight.
Seven people died moving something that spoils.