Von Rosen's involvement in Africa did not end with the Congo Crisis. He gained international fame seven years later when he flew relief missions for aid organisations into war-torn Biafra, a breakaway republic of Nigeria.[4] These flights included flying a DC-7 from São Tomé to Uli at only a little above sea level in August 1968.[6]

Disgusted at the suffering the Nigerian government inflicted on the Biafrans and the continuous harassment of international relief flights by the Nigerian Air Force, he hatched a plan in collaboration with the French secret service to strike back at Nigerian air power. He imported five small civilian single engine MFI-9 planes produced by Malmö Flygindustri, at that time owned by SAAB, which he knew could also be used for a ground attack role in warfare. He had the planes painted in camouflage colours and fitted with license manufactured 68 mm SNEB type rockets, and proceeded with a crew of two Swedes and two Biafrans to form a squadron called 'Biafra Babies' to strike the air fields from which the federal Nigerian Air Force launched their attacks against the civilian population in Biafra. On 22 May 1969, and over the next few days, von Rosen and his five aircraft launched attacks against Nigerian air fields at Port Harcourt, Enugu, Benin and other small airports. The Nigerians were taken by surprise and a number of expensive jets, including a few MiG-17 fighters and three out of Nigeria's six Ilyushin Il-28 bombers, were destroyed on the ground.[7] The Igbo intellectual Fola Oyewole who fought for Biafra recalled of all the Westerners who served with the Biafrans that Rosen was the most idealistic and the one who cared about the Igbos as a people the most.[8]