A Welcome to Britain, 1943 (US Army information film)

As most Americans had never lived outside the United States this film made by the US Army was intended to introduce American troops to British society, culture and political system

The main culture shock for white soldiers from the south was British communities rejecting racial segregation for instance:

“Local resident Gillian Vesey recalled how, as a young barmaid at the Olde Hob Inn, she stood up for African American soldiers against attempts by white Americans to impose discriminatory practices in the pub, insisting that the American white soldiers wait their turn rather than expecting to be served before their black colleagues…”

Further reading:

Black troops were welcome in Britain, but Jim Crow wasn’t: the race riot of one night in June 1943