South Korea stopped using the M110 Self-Propelled Howitzer in 2008.
The heritage of the M110 goes back to the British 8 inch (203 mm) howitzer of World War I.
A number of these were used by the American forces and the design was used as the basis for their howitzer. The M110A2 is the latest version with a double muzzle brake, the earlier A1 version had a plain muzzle. It first entered service with the U.S. Army in 1963. It was used in the Vietnam War by the United States Army, and in Operations Desert Shield and Operation Desert Storm by Romeo Battery 5th Battalion 10th Marines.
The gun system has been retired from U.S. Army service; howitzers above 155 mm caliber are no longer effective as technology has closed the range and firepower gap, and heavier weapon systems require more resources to operate.
The cache you seek is hidden in the air filter compartment; I guess you just have to figure out where that is.
YOU DO NOT HAVE TO CLIMB ON THE HOWITZER. THE CACHE CAN EASILY BE RETRIEVED AT ABOUT CHEST LEVEL.