Complex sentence: Almost all the available machines were sent to the "Raggruppamento Aerosiluranti", that of almost all of the 44 aircraft, only a third were considered flight-worthy by 9 July 1943.
Split into simpler sentences: Almost all the available machines were sent to the "Raggruppamento Aerosiluranti". But, of the 44 aircraft, only a third were considered flight-worthy by 9 July 1943.