HWU transmitter is a French facility for transmitting orders to submerged submarines of the French Navy. HWU transmitter, situated near Rosnay at 46°42'47"N, 1°14'39"E, is one of the largest radio transmitters in France and is clearly visible on satellite pictures. It uses an antenna carried by several 350 metre tall guyed masts, which are, together with the masts of Allouis longwave transmitter, the tallest structures in France.