After Mother Base's destruction, Huey went underground. He was eventually absorbed into XOF's ranks, being made chief engineer for a new Metal Gear that was being developed in Afghanistan. The Soviet Union financed and supplied resources for the project, leading Huey to believe he was working for the Soviets rather than Cipher. It was stored in a previously Soviet-controlled hangar behind the Serak Power Plant for most of its development, but was occasionally moved to OKB Zero as well. Due to its rushed development, the design of Sahelanthropus could not allow anyone other than a child to man the vehicle, as the cockpit was meant to house an AI pod instead. This resulted in a falling out between Huey and Strangelove, as he decided to use his toddler son, Hal, as a guinea pig to test the machine, something the latter vehemently disagreed with. This ultimately resulted in her death via suffocation by being trapped inside The Boss AI's casing by Huey.