Tank Gunnery in Eastern Korea

ALONG the eastern front in Korea, armor, distasteful as the thought may be, is cast in the role of front line artillery. Both in the Punchbowl sector and in the Mundung-ni Valley, the only movement of armor was onto and off the MLR.

In this entirely different part that armor has to play on this sector of the front, several little-thought-of difficulties were encountered and overcome. They should prove of interest to all Armor officers.

The absence of enemy armor activity on the eastern front leaves armor only bunkers, gun positions, trenches and small groups of enemy personnel as targets. Especially in the eastern section of the Punchbowl, tank targets are far beyond the accredited accurate range of the 76mm M1A2 mounted on the M4A3E8 tank with which this company is equipped.

Effects of Temperature Variation

It was standard practice, on line, to keep 9 extra rounds of HE on the turret floor as a supplement to our basic load. When shooting at targets at a range of 4,000 yards or more, it was found that a definite increase of approximately 100 yards was necessary when we switched to ammunition from the turret wells. This was caused by the slightly lower temperature of the rounds in the wells as opposed to those lying on the turret floor. This lessening of range was especially noticeable whenever ammunition from our storage bunkers was used. It is suggested that, whenever possible, ammunition from a common source be used to minimize correcting ranges due to temperature variation of shells. There are few occasions when this cannot be done with armor on the MLR. This factor of range variation is only applicable during the extremely hot months of June, July and August.

Probably the most frequent target that the tanker will be called upon to destroy is the bunker. In general all that can be observed of this kind of installation is a small aperture. Often this kind of target can be located only by observing personnel entering and leaving a certain area that may appear to be solely a group of bushes or small trees. For destruction of a target of this type it is recommended that, if one cannot see an aperture, the tank use HE to expose aside or an aperture, then place APC at the point about a yard below the center of the mass or aperture. This will crack the foundations and allow HE (delay) to clear out the walls and collapse the ceiling. If it is impossible to do this due to an extremely heavy construction, WP should be placed in the aperture for incendiary and anti-personnel effect.

The North Korean and Chinese forces have a habit of constructing numerous dummy bunkers, which are built solely to cause depletion of our ammunition supply. It has been found that the most effective way to deal with this sort of object is to damage the bunker, not to destroy it. After this has been accomplished, the subject bunker and all approaches should be kept under constant observation to check on any rebuilding or traffic into or out of it. If an appreciable amount of activity is noticed in or around the bunker it should be dealt with as any other installation of that kind.

HE—WP Variations

Although the firing tables of the 76mm gun state that the shells HE, M42A1, and Smoke, WP T13E2, are identical in so far as ballistics are concerned, this was not found to be true at long ranges in actual combat use. Adjustment of HE and WP proved that a definite range decrease was necessary to bring the WP to the point of HE impact. In firing at targets at a range of 3,000 yards or more it was necessary to decrease the range by 50 yards to place the WP on target. At targets within the normal effective range of the 76mm gun, this variation was not too noticeable, but as I stated before, the majority of our targets were beyond the accredited effective range.

Replacements from the States were found to be generally unfamiliar with indirect fire adjustment. We were forced to train them on line in the use of the M9 Quadrant and the Azimuth Indicator. A knowledge of these instruments is indispensable inasmuch as the majority of adjustment was made by the platoon leader from a battalion or regimental observation post and the gunners were unable, in a large number of cases, to make an adjustment fine enough with their direct fire sights. It has been stressed in all gunnery training that a finer adjustment than 50 yards was impractical with the tank gun. When firing at OPs, which were usually placed on top of ridge lines, an adjustment of 25 yards or even less had to be made to insure a target hit. Many times an adjustment of 50 yards would place the projectile over the ridge, while the same size of the projectile, if not increased, would be well below the target. These situations necessitated an addition of 25 yards or less to obtain a target hit.

Concrete piercing fuses were available to all platoons in the company and were used both in the Punchbowl and the Mundung-ni Valley. Contrary to popular opinion, the use of concrete piercing fuses does alter the ballistics of the M42A1 shell. Whenever we replaced the PD M48 fuse with the CP T105 fuse it was necessary to increase the range to obtain a target hit. A general rule of thumb that proved to be practical was to make the same adjustment as if we switched to APC with a muzzle velocity of 2600 FPS. As a check on my findings, I inquired of Lt. S. Randall of C Battery of the 21st AAA Battalion, how he observed the effect of the fuses. (We supply his 90mm gun with the CP T105 fuse.) He stated that he was forced to make approximately the same adjustment when firing this fuse. We only used this fuse against rock walls and concrete bunkers, due to the fact that it must strike a very hard object to detonate. When using these fuses the best results were obtained by first clearing all logs and dirt away from the object with HE. This was necessary, due to the fact that the shell would tend to slow up before striking the actual concrete or rock and thus fail to strike hard enough to detonate.

Dispersion Due to Overheating

Sustained firing at long ranges will have a noticeable effect upon the accuracy of the tank gun. Firing at over 3,000 yards, if continued past 15 rounds, will tend to become erratic and result in a waste of ammunition. The normal dispersion pattern was greatly elongated almost to the point of impracticability due to the overheating of the gun. A method that we devised that proved very effective was to use one tank to initially take the target under fire. As soon as the dispersion pattern became stretched so as to make adjustment impossible, a second tank that had been observing the firing would take over the target. This tank would obtain the exact range from the first tank by radio and be able to place the first round close to the target. Of course, the rate of fire at which the gun would overheat is entirely dependent upon the rate of fire, and individual platoon leaders would have to work that out for themselves.

In general, our tank positions were on the skyline in hull defilade and were not moved out of firing position, except for maintenance. This, of course, goes against basic armored doctrine almost 100%; however, a careful study of the reasons behind this and the advantages gained from so placing our tanks will, I believe, show that more is to be gained from this than is lost.

In the first place, by having our tanks on the skyline we thus throw upon the enemy the same problem that we encountered in shooting against their OPs. Any rounds that are short of our tanks will fall below them and cause no damage. Any overs will fall into the valley to our rear and will be impossible to adjust. When you couple this with the fact that our tanks can be firing back at the opposing gun within 3 or 4 rounds, one can see the advantages to this method.

Probably the strongest argument that I can advance in favor of leaving our tanks in firing position constantly is the rapidity with which we can engage targets of opportunity. On one occasion in the Mundung-ni Valley I was able to put an HE shell in the middle of a group of Chinese 35 seconds after they had been observed from the Regimental OP. No other weapon on the MLR can engage a target as rapidly and effectively as a tank.

Adaptability of Armor

As many tank officers have realized, Korea is not particularly well suited to armor. However, if there are U. S. troops operating in any terrain, armor can operate in that country. It is true that we cannot operate in the manner that we would like to, but adaptability is one of the strong points of armor. In Korea, under adverse conditions, armor has again risen to the occasion and proved its indispensability as a member of the combat arms.

FIRST LIEUTENANT SETH WIARD, JR., is assigned to the Tank Company, 14th Infantry Regiment, 25th Infantry Division stationed in Korea.