Dali Atomicus is the famous 1948 picture of Dali and cats and water by Philippe Halsman
According to this interview with National Geographic Society photographer Chris Rainier, Halsman used Tri-X film:
But according to Kodak, Tri-X wasn't invented until 1954!
and of course Tri-X TX400 is not available in sheet form (currently).
So what did Halsman use?