Under the General Command of the Air Forces, two subordinate commands were established, these being the Command of the Operational Air Forces and the Air Forces Instruction and Training Command. In campaign, the air forces would constitute formations designated "air forces in operations", which would include groups headed by lieutenant-colonels, squadrons headed by majors and flights headed by captains. The newly created squadron ("esquadra") replaced the flight ("esquadrilha") as the main tactical air unit, with a standard fighter squadron including usually 25 aircraft, comparing with the 15 of the previous fighter flights. It was foreseen that the groups could be grouped in groupings ("agrupamentos") or regiments headed by colonels and in air brigades headed by generals. The supreme command of all air forces in operations would be assumed by the Chief of Staff of the Air Forces. The personnel of the Military Aeronautics was divided in two separate branches, these being the Land Air Forces ("Forças Aeroterrestres") and the Naval Air Forces ("Forças Aeronavais"), with these last being responsible to assure the air forces of cooperation with the naval forces. While the Land Air Forces were fully integrated in the Military Aeronautics, the Naval Air Forces had a special status, continuing to be partially linked to the Navy. This branch was made of naval personnel detached from the Navy in extraordinary deployment, except the sergeants aviators and some other specialised personnel non existent in the Navy. The special status of these personnel meant, that besides continuing to be part of the Navy, their members had naval ranks and wear naval uniforms. The third anniversary of the independent air branch was marked by, probably, the most serious disaster of the Portuguese military aviation. On 1 July 1955, a formation of 12 F-84G jets was flying over several Portuguese cities, as part of the anniversary commemorations, when it entered in a group of low clouds over Coimbra, with eight of the aircraft ending up in hitting the Carvalho mountains near Vila Nova de Poiares, causing the death of the eight pilots. On the 7 July 1955, Kaulza de Arriaga is appointed as the first Under-Secretary of State of the Aeronautics. This Army engineer officer will mark the deep development of the air branch. After the experience acquired in four years as an independent branch of the Armed Forces, the air forces suffer an important reorganisation, through the Decree-law 40949 of 26 December 1956.