Tank Bumps: A New Concept in Obstacle Employment

M60A3 used in tank bump test exposes its belly as it climbs berm. Captain Stephen J. Ressler In early 1969, Colonel Thomas L. Beale, then a captain in command of B Troop, 1-1 Cavalry Squadron, watched anxiously as his tanks maneuvered across the rice paddies of the Republic of Vietnam. He discovered that the low earthen dikes which.crisscrossed the paddies severely hindered the movement of his armored vehicles, and that tanks could cross them only at very low speed, or risk breaking several torsion bars in the process. Of even greater concern was the perilous orientation of the tanks as they crossed the dikes. As each vehicle traversed a dike, it presented a very lucrative target to any enemy antitank weapon within range. While ascending, the vehicle exposed its relatively thin belly armor well above the level of the dike. While descending, it offered the enemy yet another effective shot, this time at its top armor. Clearly, he noted, the dikes not only slowed him, down, but made him afar better target, as well. Seventeen years later, Colonel Beal has not forgotten the effect of those seemingly innocuous dirt berms on the maneuverability and vulnerability of his tanks. Now, as the commander of the First Brigade, Eighth Infantry Division (Mechanized) in USAREUR, he has taken the initiative to use this effect to the brigade’s advantage. In response to recent significant improvements in Soviet armor capability, he directed his brigade engineer to explore the feasibility of using simple manmade emplacements to produce the same effects on tracked vehicle maneuverability as did the paddy dikes in Vietnam. His intent was to develop a linear, engineer-emplaced obstacle which would negate improvements in Soviet armor by causing enemy tanks to expose their most vulnerable areas - top and belly - to direct fire. It would be developed as an alternative to the tank ditch, since it would require the same engineer digging equipment to construct. In keeping with the simplicity of the concept, the proposed new obstacle was dubbed, simply, the “tank bump”. Though the concept of the tank bump is new, it reflects two well-established principles which are fundamental to the effective employment of obstacles in the defense. First, it reinforces the axiom that all obstacles must be covered by fire. It would be pointless to expose the vulnerable portions of an enemy tank if we did not expect to engage that tank with direct fire at that moment. Second, the concept recognizes that obstacles alone cannot stop a determined attack; rather, they support the defense by delaying and disrupting the attacker as he is being engaged, so that he can be engaged more effectively ARMOR: The Magazine of Mobile Warfare 25

How To Do It: * Process requires either two bulldozers or one bulldozer and a CEV or scoop loader. * Bulldozer blade is set at appropriate angle to cut V-shaped ditch. * Second bulldozer or other bladed vehicle works across ditch from shallow t o deep side, striking off spoil and building berm on friendly side. Two bulldozers working together to cut a tank bump obstacle. One cuts the V-shaped ditch while the other builds the berm. _ _ r -.. * - a *--gcr * * A bulldozer must be used to cut the ditch because its blade can be angled to create the V-shape needed.

and for a longer period of time. Tank bumps illustrate this point, because they are.not intended to stop the enemy. In fact, they can be effectively employed only if they are crossed. Thus, although tank bumps represent a significant departure from normal obstacle types, they are totally conventional in their employment. The criteria established for the development of tank bumps were Tank bumps should be easily emplaced, using combat engineer equipment currently available in the division. Their rate of emplacement should be significantly faster than that of standard tank ditches of rectangular cross-section. When traversed, tank bumps should cause an enemy tank to expose its belly or top armor long enough for a friendly gunner to aim and fire his weapon accurately at the exposed area. Tank bumps should not present such an imposing obstacle that they cause the enemy to attempt to breach or seek bypass. They must be traversed to be effective. Using these criteria as a basis, the Brigade Engineer Section conducted a series of experiments on the construction and effectiveness of tank bumps on 9 and 10 September 1985, at the brigade’s local training area (LTA) in Mainz-Gon-ANTIofANK MINES simple: I w F Extent of tank’s vulnerability to a belly shot is apparent in this photo of test M60A3 climbing the berm. The advantage would increase if friendly forces were level with or below level of the berm. senheim, Germany. The brigade’s normally associated direct support engineer company from the divisional engineer battalion supported the tests with two D-7 bulldozers; 4th Battalion, 69th Armor provided an M60A3 for evaluation of the completed tank bumps. It should be noted that the initial tests were very limited in scope. The small size of the LTA and the homogeneity of its soil dictated limited objectives: to determine the optimum configuration of the tank bump, to calculate the rate of emplacement, to evaluate the effectiveness of tank bumps as they are traversed by a tank, and to determine the degree to which their effectiveness is degraded by subsequent passes through the same path. Taking into account the tradeoff between an obstacle’s effectiveness and its emplacement time, the Bri- ARMOR The Magazine of Mobile Warfare 27

Tank bump also exposes a tank’s thinner top armor to killing shots as it descends the berm. gade Engineer determined the optimum configuration to be the triangular ditch-berm arrangement shown in Figure 1. Two D-7s constructed the tank bumps, working as a team: one cutting the ditch with an angled blade, the other “striking off’ the spoil and building the berm on the friendly side in the process. The rate of emplacement was approximately 250 meters per hour in relatively soft, sandy soil. A dozer must be used to cut the ditch because an angled blade is required to create the V-shape; however, a combat engineer vehicle or scoop loader could substitute for the second dozer with no significant decrease in efficiency. At this point, the designation of the friendly and enemy sides of the tank bump was, in fact, arbitrary. During evaluation tests, a tank would traverse the emplacement in both directions to determine the most effective orientation. Evaluation of the effectiveness of the tank bumps consisted of four separate tests, all conducted with one M60A3 tank. First the tank crossed a single bump, moving from the enemy side to the friendly side (first through the ditch, then over the berm.) Then it crossed in the opposite direction. Third, it made multiple passes along the same path in both directions to determine how much the bumps are degraded by continued traffic. Finally, the tank traversed a “bump course” - a series of three parallel tank bumps. The results of the tests were promising. When the M60A3 crossed a tank bump from the enemy side to the friendly side, it exposed its belly very effectively as it climbed the berm. Even though only a portion of the belly projected above the top edge of the berm, it is important to note that the berm itself would not stop (or even slow down) a sabot round. In effect, the portion of the tank’s belly which was hidden by the berm was still exposed to direct fire. The tank’stop was not as effectively exposed, however, since the tank could descend the friendly side of the berm much more quickly than it could climb the enemy side. When crossing in the opposite direction, the tank exposed its belly almost as effectively as it had in the first test. Unlike the first test, though, it also exposed its top armor for a significant period of time - 5 to 10 seconds. As the tank descended the berm, no matter how slowly it moved, its lower frontal armor dug into the bottom of the ditch, and the vehicle had to plow its way out of the ditch in order to continue moving forward. On the average, it took 10 to 15 seconds to traverse a single tank bump in either direction. The tank commander noted that he could not have crossed the bumps any faster without damaging the tank‘s suspension system. He added that he could not possibly have employed his main gun at any time while crossing. Subsequent tests indicated that the effectiveness of tank bumps was not degraded by consecutive passes through the same path. On the first pass, the tank tended to compact the berm, making it just as effective on the next pass. Employing three parallel tank bumps in depth significantly improved the effectiveness of the obstacle. The first bump in the series reduced the tank’s momentum, thus making it more difficult to traverse each subsequent bump. Upon completion of testing, an analysis of the results and a detailed debriefing with the tank crew of the test vehicle yielded a number of conclusions: Most importantly, the relatively short period of time it takes a tank to traverse a tank bump dictates that this obstacle cannot be effectively covered by TOW or Dragon missiles. Because of their lengthy time of flight, wire-guided missiles could not engage enemy tanks during the brief period when their bellies or tops are exposed. Clearly, tank bumps must be used in support of tanks. Tank bumps oriented so that an enemy tank must cross first the berm, then the ditch, appear to be most effective in exposing both the tank‘s belly and top; however, tank bumps oriented in this direction are also the most easily breached. An enemy engineer vehicle or blade tank could simply plow the loose earth berm into the ditch to create a lane. If the orientation is reversed, breaching is considerably more difficult. Because tank bumps are intended to be an alternative to tank ditches, it is useful to compare certain aspects of the obstacles. Note that tank bumps are significantly - 28 ARMOR: The Magazine of Mobile Warfare shallower (see Figure 1). As a result, their emplacement rate is three to four times faster. Because a tank bump’s ditch is less than one meter deep, it would be especially useful in an area where tank ditching is impossible, due to the proximity of bedrock to the surface. (Bedrock less than one meter from the surface is a common condition in West Germany.) Unlike tank ditches, tank bumps are not nearly deep enough to be used as expedient fighting positions by an advancing enemy. Based on these conclusions, the brigade has developed a recommended configuration for a tank bump course which takes best advantage of the favorable characteristics of this obstacle (Figure 2). The course can be emplaced with the same amount of engineer equipment hours as a standard reetan-gular tank ditch of the same length. It is designed to achieve the following effects: An enemy tank crosses the first two bumps. exposing his belly twice to friendly fire. In this orientation, the bumps are easier to traverse than to breach, so he would most likely attempt to cross, rather than bring his engineers forward. The third bump is reversed, so he exposes both his belly and top as he crosses. While the tank bump in this orientation is more easily breached, the enemy tank is already exposed to direct fire with tank bumps to his front and rear. Breaching equipment would have to cross the first two bumps before it could reach the third. 0 As the enemy encounters the third tank bump, he also encounters the leading edge of an antitank minefield. The first two bumps disguised the presence of the mines, so he probably was not aware of their existence until he encountered the first one. Now, even if he crosses the third tank bump without being hit by direct fire, he must still breach a minefield. His primary means of minefield breaching - tank mounted rollers and plows - would find it extremely difficult, if not impossible, to move across the three tank bumps to reach the minefield. 0 During the entire period it has taken to cross the obstacle, the enemy has been unable to fire his main gun. While tank bumps have shown a c e 2 Tank bump: can. Loose! protection t good deal of promise, it would be hasty to fully embrace the concept based solely on the testing done to date. Those tests, though they fully accomplished the established objectives, were not without several severe limitations: Initial tests were done in relatively soft soil. Emplacement times in different soil types may be somewhat slower. The concept demands that friendly tank crews are able to acquire and engage their targets with pinpoint accuracy during a very short span of time. The tests did not address the feasibility of such engagements under battlefield conditions. The tests were conducted on ground which was essentially level. Yet it is reasonable to expect that effective employment of tank bumps will be heavily dependent on the height of the friendly battle position and the slope of the kill zone on which the bumps are emplaced. If the battle position is significantly higher than the kill zone or if the kill zone is on the forward slope of a hill, “top shots” will be greatly enhanced, but it may be difficult, if 1 1 1 5 cannot provide defilade for attackers, as tank ditches sometimes soil is easily penetrated by modern APFSDS rounds and offers little o hull. not impossible, to create a “belly-shot”. Nonetheless, the initial tests have convinced Colonel Beale that tank bumps do, in fact, have the potential to accomplish their desired objective of exploiting the vulnera-bilies of Soviet tank armor. That potential can only be realized through further testing - during tactical maneuver, in different types of soil, on irregular terrain, during periods of limited visibility. In the months ahead, the First Brigade will continue to test, develop and refine the concept, and will ultimately make tank bumps a viable part of its General Defense Plan.

CAPTAIN STEPHEN J.

RESSLER isassignedto HQ, 8th Infantry Division, FRG,as brigade engineer. His CO. Colonel Thomas L-Beale, developed theconcept whileob-serving armor difficulties traversing drainage ditches in Vietnam and assigned Captain Ressler to investigate the usefulness of the technique as a tank obstacle in

USAREUR.

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