Captain Zarlo was a Starfleet officer who was assigned to replace James T. Kirk as captain of the USS Enterprise on stardate 1929.13, when Kirk was sent on a anti-Klingon mission on the planet Mobia.
Zarlo ordered a "nuke malfunction drill" each day for five days, the ship set a new record for the drill in starship service but Zarlo wanted the crew to perform better. Later, the Enterprise received a coded message that Captain Kirk has disappeared and Zarlo told the crew the truth about Kirk's secret mission. They demanded that Zarlo take the Enterprise to Mobita, in order to help search for Kirk. But, Zarlo refused and was only backed up by Spock.
However, when the crew threatened to mutiny, Zarlo agreed to turn the ship toward Mobita. When the Enterprise arrived in orbit around Mobita they found a Klingon warship in orbit. The Enterprise fired a warning shot off the bow of the Klingon cruiser, and the ship quickly left the area - abandoning the Klingon soldiers on the surface. As the Enterprise left orbit, Zarlo told Kirk, "I'd trade six months leave for a crew that would stand by me as yours does!"
Zarlo's time as Enterprise captain was among the shortest in length out of any of the captains of that vessel.