I'm not entirely sure what the "US" pin is. In the Army, both today and in WWII, officers wear that pin on the lapel. However, I don't think the Navy does currently, and I can't see on Google images where that pin would have gone during WWII. Nevertheless, it's almost certainly some sort of generic uniform insignia that everyone, or all officers, wore.

The wings are US Navy aviator wings, indicating that he was a pilot.

The purple ribbon is the Purple Heart, and the oak leaf in the center represents a second award of it, so your grandfather was wounded in action twice.

The center ribbon is the Asiatic-Pacific Campaign medal, which was awarded to anyone who served in the Pacific during WWII. The star in the center is a service star and indicates that he actually took part in combat in addition to serving in that theater of operations.

The ribbon on the left is the American Campaign Medal, which means that he served somewhere in the American Theater of Operations, as well, likely on convoy escort or anti-submarine operations.

The ribbon on the right is the Navy Rifle Marksmanship Ribbon