Gallium Nitride (GaN) devices are foreseen as the next generation of RF power transistor technology in the millimeter wave range. A number of groups (HRL, Triquint, UCSB, and Fujitsu) have demonstrated the unique combination of higher power, higher efficiency and wider bandwidth available with GaN as compared to competing GaAs and Si based technologies. In this frame, a new heterostructure based on high quality AlN/GaN has been developed and enables to boost transistor carrier density 2-3 times higher than AlGaN/GaN HEMTs, while offering high aspect ratio (Lg/a) needed for millimeter wave operation due to the possibility to use ultra thin barrier. Using this novel double heterostructure AlN/GaN/AlGaN on Si, developed in collaboration with EpiGaN, IEMN has already demonstrated achieved state of the art results which have shown: *Cut-off frequencies Fmax about 200 GHz together with a voltage handling of more than 100V which allow to reach very high power density in Ka band (2.5W/mm @40 GHz). *Very low leakage currents, high gain, reduced trapping effects which have led to the lowest Noise Figure ever measured in Ka band with GaN HEMTs (NFmin=1.2dB @40GHz). In addition a preliminary reliability study developed with the University of PADOVA has shown quite promising results in terms of stability and robustness with several hours of measurements on 100nm gate length devices. These first reliability results demonstrate that the reproducibility is good enough to foresee the realization of complex circuits in Ka band. The CROCUS project aims at the design, realization and test of robust circuits in Ka band based on the AlN/GaN on Si technology with outstanding performance for civilian and military applications. This paves the way to a European source of reliable millimeter wave MMIC GaN on Si circuits telecommunication and radar systems. This project proposes to design, realize in hybrid integration and test some key Ka band circuits such as power amplifier (HPA), Low noise amplifier (LNA) and mixer, using EpiGaN epitaxies. These circuits will be developed with respect to Thales communication (military communication systems) and BLUWAN specifications (Civilian LMDS & Satellite applications). IEMN, XLIM, THALES Com and BLUWAN will join their efforts and combine their competences to reach the ambitious goals of this project which should lead to a real technological breakthrough in terms of power, efficiency, linearity and self protection. Even though Thales is not an official partner of this project the society is interested in following it and is willing to provide operational specifications according to their military applications and to promote an industrial development of this technology (Cf joint letter of Thales)