What is the author's style in Mister Roberts by Thomas Heggen?

Symbolism as a technique involves using an object, event, or person to represent an alternate meaning. For example, the small palm tree that sits in a five-gallon can outside the captain's cabin symbolizes the smallness of the tasks in which the ship is engaged. Roberts explains that the palm tree was awarded to the ship for "delivering more toothpaste and toilet paper than any other Navy cargo ship in the safe area of the Pacific." It is not the sort of award that men fight to win during a war. To the men, it is a reminder of their own boredom and sense of frustration and futility. The fact that the captain reveres his little trophy gives it an added significance: it represents the captain's vanity, his obsession with insignificant things, and his ambition, since he wants to use his ship's success as a stepping stone to attain the rank of commander.