Thanks so much to US-subs for his archive photos. One in particular was of the 4.2" Recoilless Mortar. I got curious and found this US Army trailing film on it. Two words, HEARING PROTECTION!!
http://www.criticalpast.com/video/6...oluene-shells_reaction-chamber_rocket-drivers
http://www.criticalpast.com/video/6...oluene-shells_reaction-chamber_rocket-drivers