Army investigators have concluded that a left-over 66-mm high explosive anti-tank round fired from an M72 Series light anti-tank weapon, or LAW, injured two maintenance workers when the round exploded April 6 at Makua Military Reservation.

The LAW was developed in the 1960s and was fired on the range until the 1980s, the Army said. Investigators could not determine when the round had been fired or by what unit.

“The safety and well-being of our soldiers, Army civilians, contractors and public visitors to our ranges and facilities is one of our highest training priorities,” Maj. Gen. Charles Flynn, commander of the 25th Infantry Division, said in an Army-produced news story. “With the investigation complete, we will redouble our hazard awareness and safety procedures to prevent tragic incidents like this from occurring again.”

Two contracted workers were conducting routine grass-cutting nearly one mile inside the south side of Makua Valley when one unknowingly contacted the round with a hand-held grass cutter, the Army and Honolulu Fire Department said.

Both contactors with the NuGate Group LLC were hospitalized. NuGate owner Jamila Stanford said a few days after the warhead exploded that the injuries were “not life threatening.”

U.S. Army Hawaii, Army Technical Center for Explosives Safety and Army Combat Readiness Center conducted the accident investigation.

Makua has been closed to all Army training and public access since the incident occurred, the service said. Training and cultural access will resume after additional mitigation measures are conducted based on the investigation’s recommendations. Makua is expected to reopen within 60 to 90 days.

Prior to the fielding of the AT-4 84-mm anti-tank weapon, the M-72 LAW was the Army’s primary shoulder-fired, man-portable, light anti-tank rocket, according to the Federation of American Scientists.

Although associated with the Vietnam War, the LAW was used in Iraq and Afghanistan and still is in inventory because of its lower cost and lighter weight than the AT-4.