“The SOFAR channel (short for sound fixing and ranging channel) … is a horizontal layer of water in the ocean at which depth the speed of sound is at its minimum” …
“The SOFAR channel acts as a waveguide for sound, and low frequency sound waves within the channel may travel thousands of miles before dissipating.” …
https://en.m.wikipedia.org/wiki/SOFAR_channel
Ladoga –a Russian armoured personnel carrier. Initially called Debut, this APC is designed for evacuation of Soviet government from Kremlin to airport under nuclear/chemical/biological attack. Ladoga uses tracks from the T-80U as well as suspension system and gas-turbine powerplant. The crew is 2 soldiers. It also has a four-seat cab equipped with a crew life-support facilities to protect the passengers against the radiological, chemical and bacteriological contamination of the environment.
https://en.m.wikipedia.org/wiki/Ladoga_APC