in world war two why did the us troops yell thunder and why was the response responce flash?

this password code was only used during the Normandy invasion June 6th 1944 mainly by airborne paratroopers who were dropped behind enemy lines early in the campaign, you will also see/hear the same passwords used in other shows/movies related to the Normandy invasion, like "the longest day" with more movie stars than can fit on one screen

btw the code was used to determine if an unknown person was friendly or not by giving the correct response

That was the challenge and password for Allied troops on D-Day. The idea was that if you heard someone on the other side of a hedge, you'd call "thunder!" If you didn't get a response, or got the wrong response, it was an enemy.

This was used to cut down on friendly fire incidents.

Those were passwords so that friendly units could identify each other. If you yelled out the password "flash" and didn't get the correct reply of "thunder" you opened up with everything you had because that meant the guys in the next shrub were baddies.

That is known as a challenge and password. We still use them and they change every 24 hours or so.

Imagine being on a perimeter in pitch darkness and a group of people approach your foxhole. You give the challenge and they should respond with the correct password or if not they face being fired upon.

no, the call was FLASH and the response was THUNDER (Band of Brothers Stephen Ambrose) because most native germans could not pronounce THUNDER correctly, the TH was missing, they pronounced it TUNDER. FLASH TUNDER bang u r shot

It was the challenge and password for that day. The next day it would have been something else.

It was code for identifying friendly forces and preventing accidental shootings.

Because Kilroy may be out there looking over the fence!