Why You Cannot Radio a Submarine Deep UNDERWATER

Your phone talks to a satellite in space, but no ordinary radio signal can reach a submarine a few meters underwater.

Radio crosses whole oceans through the air. So why does saltwater stop it almost the instant it gets wet?

Seawater is full of dissolved salt, making it a decent electrical conductor. When a radio wave hits it, the wave stirs up tiny currents that drain its energy almost at once. A normal high-frequency signal dies in less than a meter. The fix is to go extremely low in frequency. Very low frequency waves reach a sub a few meters down, and extremely low frequency waves, some just tens of cycles per second, can sink hundreds of meters. But that depth comes at a brutal cost in speed.

Here is the cruel trade: those deep-reaching waves carry almost no information. An extremely low frequency signal is so slow that just three letters can take around fifteen minutes. You reach the deep, but only whisper to it.

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