challenge and response

During Operation Overlord soldiers were trained to use a "challenge and response" system in order to identify friendly forces in situations were they could not make visual contact.

Captain Miller's Ranger squad used this system while passing through the town of Neuville during their search for Private James Ryan.

First Army Passwords

Day Challenge Password
June 6 D-Day flash thunder
June 7 D+1 thirsty victory
June 8 D+2 thirsty victory
June 9 D+3 thirsty victory
June 10 D+4 weapon throat
June 11 D+5 weapon throat
June 12 D+6 weapon throat
June 13 D+7 wool rabbit
June 14 D+8 wool rabbit
June 15 D+9 wool rabbit

Fact vs. Fiction

The proper order of the challenge and response is reversed in the film. The proper challenge on D-Day would have been "flash," the password "thunder," and the countersign "welcome."

The challenge and response words were changed every three days in the First Army, which further confuses the use of this system in the film, since the Rangers were in Neuville sometime between the 9th and 13th of June. The 101st paratroopers would not have been using flash/thunder/welcome by that time.