What insignia represents an O-4 in the Navy?

In the United States Navy, the rank of O-4 is represented by the insignia of a gold oak leaf. This insignia signifies the rank of Lieutenant Commander. The gold oak leaf serves as a visual representation of the officer's position, distinct from other ranks in the Navy hierarchy.

For context, the other insignias correspond to different ranks: a silver spread eagle represents an O-5, which is a Commander; one silver oak leaf represents an O-5 in other branches of the military, such as the Army and Air Force; and one silver bar symbolizes an O-3 or Lieutenant. Therefore, the gold oak leaf is specifically linked to the rank of Lieutenant Commander, making it the correct choice in this question regarding O-4 rank insignia in the Navy.