Let's fast forward to the present and shine more light on GPS while trying to understand how Lamarr's and Antheil's work relates to the gadgets we see today.

The old school method of transmitting data is to squeeze as much data into as narrow a band as possible. Somebody snooping the radio bandwidth might see something like this:

This would be easy to spot and susceptible to jamming.

One of the curious properties of spread spectrum communications is that, given the same transmit power, the same information divided across multiple frequencies will be more spread out. If the signal is spread wide enough, the signal can actually vanish into the noise and become indistinguishable.

With spread spectrum transmissions you need a way to separate the data from the noise. Imagine if you will, spreading a foot high pile of pepper in a sandbox. It might seem the pepper is irreversibly lost in the sand. But because you know there is pepper in the sand and if by some means you can recover the pepper, say by blowing on the sand, it would be possible to eventually reconstruct the original pile of pepper. I hope that makes sense, as these are the sorts of analogies one writes while eating.