A Morton Thiokol Inc. exhaust nozzle is among the parts of the Trident II missile being overhauled after the weapon, during its inaugural test launch from a submarine on March 21, went out of control and exploded.

Lt. Janet Mescus, a Navy spokesman at the Pentagon, said analysis of data and parts recovered from the failed test indicated the missile went out of control for two reasons.One of the problems originated in the mechanical link that transmits direction commands to the first-stage exhaust nozzle, which pivots to control the missile's direction. The second involved the timing and degree of the nozzle position commands as pressure is building in the motor early in the missile's flight.

The three-stage, multiple-warhead rocket, which will be the Navy's most powerful weapon, cartwheeled out of control and exploded four seconds after launch off Florida's Cape Canaveral.

Morton Thiokol spokesman Rocky Raab said he did not know if the nozzle failed, but among other changes requested by the Navy, "it is reasonable and prudent to reinforce the nozzle as well."

Morton Thiokol and Hercules cooperate in building the rocket's first and second stages. Neither Utah company produces the actuators that mechanically direct the first-stage nozzle cone or the missile guidance system.