"The foam you can see there (as well as the bluey looking foam later on) isn't really designed to be anechoic to sound but rather anechoic to electromagnetic waves. It does end up being somewhat anechoic to sound anyway due to the dense construction but that's a side-effect. So this means these chambers were probably for testing radio or radar equipment.

NB Elsewhere you have a picture of some grey foam with cones in alternating alignment -- this is anechoic lining for a sound chamber."

John