HWU transmitter is a French facility for transmitting orders to submerged submarines of the French Navy

French Navy

The French Navy, officially the Marine nationale and often called La Royale is the maritime arm of the French military. It includes a full range of fighting vessels, from patrol boats to a nuclear powered aircraft carrier and 10 nuclear-powered submarines, four of which are capable of launching...

. HWU transmitter, situated near Rosnay

Rosnay, Indre

Rosnay is a commune in the Indre department in central France.-References:*...

 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.

HWU transmitter works on 18.3 kHz, 20.9 kHz and 21.7 kHz. Its transmissions can be easily received in Europe when the transmitters are active by using a PC soundcard connected to a receiving coil and FFT software. Although the signals are very easy to receive, it may be impossible to decipher them without knowing the cipher

Cipher

In cryptography, a cipher is an algorithm for performing encryption or decryption — a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. In non-technical usage, a “cipher” is the same thing as a “code”; however, the concepts...

 and key

Key (cryptography)

In cryptography, a key is a piece of information that determines the functional output of a cryptographic algorithm or cipher. Without a key, the algorithm would produce no useful result. In encryption, a key specifies the particular transformation of plaintext into ciphertext, or vice versa...

 used in the communications.

See also

• List of masts
• List of tallest structures in France