This is a rare example of an original World War II Navy Oerlikon 20mm Cannon cutaway motorized training device that was manufactured by Reflectone Corp. of Stamford, Connecticut. This gun, which is typically referred to as just "the 20mm Oerlikon", became probably the most effective anti-aircraft cannon of World War II. During the war it was also used in various forms by the British, Americans, German and the Japanese. It functions as a an advanced primer ignition blow back with a huge recoil spring mounted around the outside of the barrel to delay recoil. 20mm Oerlikons were used on every type of Navy ship from tugboats to PT boats, minesweepers, all the way up to aircraft carriers and everything in between. The German Army even employed them in a wheeled/towed version with twin mounts, and the Japanese used an almost identical version in their fighters, such as the famous Zero. So obviously these are a very historically unique and valuable weapon. Originally they used an electronic sighting system mounted on top of the gun that provide the appropriate lead and angle to make effective kill shots. The top of the deactivated cutaway receiver is marked "20mmM.G. MECH./MK.2/SER. No. 82287". The barrel is marked on top "20MM/MK4/MOD1/713559/SMOC NOP SC". The large wood mount contains motorized linkage inside, and has a data plate on top with a Department of the Navy Office of Naval Research logo above "SPECIAL DEVICES CENTER/SECTIONALIZED 20 MM ANTI/AIRCRAFT GUN, MOTORIZED, MK-4/DEVICE NUMBER/11-D-4d/CONTRACT NUMBER N140S-96975A SERIAL NUMBER 188 (US)/MANUFACTURED BY/REFLECTONE CORP./STAMFORD, CONN." in nine lines.