Initially a new experimental unit was formed at Fort Benning, Georgia, the 11th Air Assault Division on 11 February 1963, combining light infantry with integral helicopter transport and air support. Opinions vary as to the level of support for the concept within the Army; some have argued that the initial tests against the context of conventional warfare did not prove promising, and, despite opposition from the Joint Chiefs of Staff, it was primarily the Secretary of Defense Robert McNamara who pushed through the changes in 1965, drawing on support from within the Pentagon which had now begun to establish a counter-insurgency doctrine that would require just such a unit. Others have put more weight on the support of newly appointed senior Army commanders, including the new Chief of Staff General Wheeler, in driving through the changes. Nonetheless, the 11th Air Assault Division assets were merged with the co-located 2nd Infantry Division and reflagged as the 1st Cavalry Division (Airmobile), continuing the tradition of the 1st Cavalry Division. Within several months it was sent to Vietnam and the concept of air mobility became bound up with the challenges of that campaign, especially its varied terrain – the jungles, mountains, and rivers which complicated ground movement.