By the spring of 1941, Pinna's forces had been effectively annihilated; in April he left Addis Ababa and followed the Duke of Aosta to the mountain redoubt of Amba Alagi, where his remaining men fought as infantry. After a weeks-long siege, he was captured by the British along with the Duke and Generals Marino Valletti-Borgnini, Luigi Frusci and Claudio Trezzani in May 1941. Pinna was then sent to India, at the Prem Nagar POW camp, eight miles east of Dehradun. On 20 December 1942 he was transferred to the United States and imprisoned at Camp Monticello, Arkansas.