You assume the sub knew they were all civilians. There was little sympathy for them after what had occurred in the war by then.
As Sledge said in “The Pacific”:
“WE WERE ALL SENT HERE TO KILL JAPS, WEREN’T WE?! SO WHAT THE HELL DIFFERENCE DOES IT MAKE WHAT WEAPON WE USE? [leans in] I’d use my goddamn hands if I had to.”
My father missed serving in WWII but served during the Korean conflict. He worked with a guy served in WWII and survived the Bataan death march. He was besides himself seeing younger people buying Toyotas and Hondas and refused to ride in one.