A method for obtaining jet fuel from diesel fuel is provided, the method comprising subjecting the diesel fuel to hydrocracking to convert at least a portion of the diesel fuel into a mixture of light hydrocarbons, kerosene, naphtha and a liquefied petroleum gas, isolating the kerosene, recovering jet fuel from the kerosene, subjecting at least a portion of the mixture of kerosene, naphtha and a liquefied petroleum gas to steam forming to obtain a synthesis gas containing hydrogen, and recycling hydrogen contained in the synthesis gas to the hydrocracking step. A modular system for performing the method is also provided.