Speech coding for security and defense apps, Why do we need very low bitrate? Options

[QuantumKnot]

Hi everyone,

I've heard that ultra low bitrate speech coding (< 800 bps) that use simple modifications to the LPC vocoder (such as segmented LPC vocoders), are of interest mainly for security and defense applications. At such low bitrates, I assume that intelligibility is the only criteria here. My question is why do we need to go to such low bitrates for defense and security? Is it because we want to reserve bandwidth for error-correcting redundancy? Or perhaps encryption? The only thing that I've read which sort of remotely justifies the low bitrate is a lesser chance of being intercepted.

If anyone can enlighten me as to why we need such low bitrates (< 800 bps) for security and defense, that would be splendid.

Thanks,

QK