At www.movietone.com you can search for newsreels containing various subjects and watch them online. There are several short films showing the S.S. Rex from 1938 and 1939 with people gambling. One shows the Rex and Texas being shut down, with some equipment being thrown overboard and cards being stepped on and ground into the floor. Shows Tony Cornero too. Another from 1946 shows the Lux with people gambling. Strangely, almost nothing on Las Vegas, except one short clip of planes landing at McCarran in the early 60's.

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http://www.movietone.com