Calibration Vs. Zeroing

I Calibration Vs. Zeroina E '1 by Captain Mark T. Hefty The M60A3 main battle tank has a complex fire control system. The current method of calibrating the M60A3 is to conduct an accurate boresight, then fire a round at a 900- meter target panel. If the round hits the target, the tank then fires a confirmation rQund at a 1,500-meter target panel. If that round hits, then the tank is calibrated. If the first round hits and the second round misses, a third round is fired at a 1,250-meter panel. If that round hits, the tank is calibrated. If the tank misses the first round at the 9O-meter panel, it is not calibrated, and the crew must check several items, such as boresight and knob settings on the gunner's control unit (GCU). The GCU feeds data into the computer, including gun tube wear, air temperature, and elevation. The crew follows the same procedures if it hits the 900-meter panel. but misses both the 1,500-meter and 1.250-meter panels. Normally, the company master gunner is in the calibrating tank, and the battalion master gunner is in the range tower. They are checking the elevation output reading from the elevation actuating arm and comparing the reading to the solution in the ammunition tablcs, which gives a mathematically calculated output reading and a small tolerance. If the tank's output reading is outside the given tolerance, the tank does not fire, and the turret mechanics check the entire fire control system for malfunctions. Inside the GCU are four very special jump knobs. Two of them control azimuth and elevation for HEAT ammunition and two control azimuth and elevation for SABOT. The knobs allow manual input of correction data to the computer. Currently, the only authorized knob adjustment is a -.8 mil elevation for HEAT ammunition. That number is derived from historical data indicating that HEAT consistently shot high. After a particularly disappointing Level I gunnery, my battalion commander looked for a solution. He asked the few (about 10) tank commanders who had qualified what they had done to be successful. Some of them said that they had adjusted their jump knobs after calibration to bring the strike of their rounds closer to center of mass of the target. The battalion commander also heard that another battalion in the division had allowed its personnel to adjust their jump knobs, and they had shot very well. Using this information, the commander came up with a plan to qualify more tanks at gunnery by making adjustments to jump knobs in a "controlled" manner. He authorized adjustments based on a two-round shot group at the 1,250-meter panel. The adjustments brought the strike of the round within a three foot radius of center mass. The tank fired a third round at the 1,250-meter panel to verify the adjustment. If the round struck within the target circle, the - 78 ARMOR - September-October 7988

"Using the "oid" way of calibrating, even if the round struck only the edge of the panels, we made no adjustments. Then, during a hasty reticle lay, if the gunner layed slightly off center of mass, the round could miss the target. 'I tank fired a fourth round at the 1,500-meter panel. If the round hit the panel, the tank was calibrated for that type ammunition. If the third round did not hit within the target circle on the 1,250-meter panel, the commander determined if a further adjustment was feasible, based on how the first adjustment moved the strike of the round. The battalion commander listened to recommendations from the respective platoon sergeant, master gunner, and company commander. The results of this gunnery were astounding. The battalion qualified about 44 tanks out of 58 on their first run on Tank Table VIII. That was about four or five times better than previously. I was the towerlrange officer in charge (OIC) for the entire battalion's calibration, and became very familiar with the sequence. I was also the range OIC at a subsequent gunnery, when the battalion qualified 54 out of 58 tanks on their first run on Tank Table VI11. the best M6OA3 tank battalion qualification rate in USAREUR. One area of concern was the number of rounds allocated for calibration. The normal allotment was three HEAT and three SABOT. The modified version required four, or sometimes five, rounds per tank, per ammunition type. We found that most tanks only needed two rounds of SABOT because of the round's accuracy. The HEAT was more difficult to balance, though. We diverted some of the Tank Table VI rounds to make up the difference. Benefits were that the crews had more confidence in being able to hit targets, and it also started the gunner closer to center mass of the target. That is to say, the strike of the round is closer to the gunner's lay. Using the "old" way of calibrating, even if the round struck only the edge of the panels, we made no adjustments. Then, during a hasty reticle lay, if the gunner layed slightly off center of mass, the round could miss the target. There is a direct relationship between our use of adjusting jump knobs and our battalion's success. Keep in mind that not every tank needed to make any adjustments, and after two battalions-worth of jump knob adjusting, the effects on round impact were very consistent. Captain Mark T. Hefty was commissioned from the USMA in 1983. He also attended the AOBC and AOAC. Assigned to the 1-37 Armor, 1st AD, in the FRG, he served as mortar platoon leader, tank platoon leader, tank company XO, and 53 Air. He is currently assigned as assistant S3 of the 2d Bde, 5th ID, at Fort Polk, LA. ARMOR - September-October I988 79