The V-3/A was a nuke-mobile built by Nuke in the late 23rd century, entering production in 2262. Two years later, Nuke were forced to issue a warning that all V-3/A's suffered from a defective 3rd diverter system, causing the coolant coils to overheat.
Lieutenant Commanders Spock and Montgomery Scott used a V-3/A to collect Captain James T. Kirk from Phobos Base to take him to rendezvouse transporter coordinates with the USS Enterprise. En route, the V-3/A broke down as a result of the diverter system defect. Scott, wrongly assuming that the V-3/A was a V-3, couldn't identify the problem, but Kirk was able to diagnose the problem so that repairs could be completed.