'Battle Cry' was a Warner Brothers war movie made in 1955. I bet this aircraft was paid for by WB as a little bit of free publicity/advertising and goodwill. I think due to the films date, the pic would the be related to the Korean War and the guys who are 'pretending' to load a desultory amount of ammo and ordnance are taking part in a publicity pic for the studio.
Here's a linky thing to the movie.
Battle Cry (film) - Wikipedia, the free encyclopedia