The broth of subsidy-era pilotless pho was given taste with MSG. During Vietnam’s postwar subsidy period, state-run pho eateries faced severe shortages of meat, rice, and other ingredients, so some served a meatless version called phở không người lái, or “pilotless pho.”
Its broth could be little more than boiled water seasoned with monosodium glutamate. MSG supplies umami, the savory taste associated with meat and long-cooked stocks, making it a practical substitute when traditional broth ingredients were unavailable. The nickname referred to U.S. unmanned reconnaissance aircraft, not to the flavor or preparation.
This was an emergency-era version, not the standard definition of pho. Traditional beef pho is built from simmered bones, meat, charred onion and ginger, and spices such as star anise, cinnamon, coriander, and clove. Fish sauce is also commonly added near the end. Modern restaurant broth therefore should not be assumed to be simply water and MSG.