As winter approached, caves were being discovered in the mountainous southeastern part of Kosovo--one of them in the Task Force 1-36 Infantry sector. The task force had learned that a cave also had been discovered in the Polish sector and, after the entrance was cleared, multiple antipersonnel mines with trip wires were found. Additionally, the cave contained a weapons cache, a much-earlier victim of a booby trap, chemical fuses, and a gas mask for a horse. This indicated the age and diversity of the cache and suggested the possibility of a chemical threat associated with caches in remote areas. Alpha Company's 1st Platoon was tasked to clear and seal the cave in the Task Force 1-36 Infantry sector and provide command and control of additional assets, as necessary. This article relates the events surrounding the demolition reconnaissance, hypothesis, and execution and the lessons learned.
Key leaders from the platoon, an explosive ordnance disposal (EOD) team, and a security detail from Alpha Company, 3/327 Infantry, which owned the sector in which the caves were found, went into the hills to conduct a reconnaissance of the cave. The route leading to the cave--about 15 kilometers of dirt road containing potholes and extremely sharp curves--was untrafficable to vehicles with long wheel bases (such as heavy expanded-mobility tactical trucks [HEMTTs], dump trucks, and mix trucks). After arriving on-site, the infantry secured the area, and sappers in mission-oriented protective posture (MOPP) Level 1 gear used AN/PSS-12 mine detectors to sweep a path to the entrance of the cave, while scanning for signs of booby traps. Once a path had been cleared, a left and right handrail was emplaced using high-visibility tape.
Sappers from 1st Platoon were then ready to begin gathering critical dimensions of the cave for a potential demolition mission. Before they could determine the inside diameter, they had to clear several feet into the cave. First, they visually inspected with a flashlight from a cleared position and then grappled into the cave as far as possible from behind a berm a few meters from the entrance. Once this was completed, the dimensions could be collected.
1st Platoon sappers discovered that the average interior diameter of the cave, which extended into the hill approximately 75 meters, was 5 feet. There were no abrupt changes in direction in the cave, and it was level with the horizon. Although the cave appeared to be constructed by man, there was no evidence of spoil or means for spoil removal. The hill that the cave extended into resembled granite in appearance, strength, and hardness.
After collecting the critical dimensions and the necessary information for the demolitions reconnaissance report, the recon team members returned to Camp Monteith to formulate their plan of attack. They established design criteria based on two demolition techniques.
The first technique was based on a combination of the Methods I and II attack on an arched, closed-spandrel, masonry bridge. Essentially, the structural integrity of the cave would be destroyed by placing a charge on each wall and one on the ceiling to create the necessary spoil to seal the cave. These three charges formed one firing system.
The second demolition technique used the premise of counterforce-charge demolitions. The challenge would be to create the required amount of spoil to seal the cave, while taking into account the amount of rock that would be pulverized into inadequate sealing material. The solution was to create a counterforce shock wave by placing three equally spaced firing systems in the cave and detonating them simultaneously. The theory was that the shock wave from the two outer charges would collide with the shock wave from the inner charge and Force the inner charge to penetrate to a much greater depth, causing a larger volume of material to be displaced. If too much force was generated, material could be blown from the cave, creating a large crater and subsequently a second entrance to the cave from above. These were the premises that were the foundation for the design of the charges.
The charge design was based on calculations in Field Manual 5-250, Explosives and Demolitions, for breach charges attacking rock. Taking into consideration the dimensions of the cave and the volume of material necessary to be produced plus the void created by rock pulverization, a 7-foot breach charge was selected. This amounted to 118 packages of C4 explosives per breach charge, 354 packages per counterforce charge, and 1,062 packages for the firing system--or 1,327.5 pounds of C4 to be detonated simultaneously (see Figure 1).
When Alpha Company personnel contacted the Engineer School to verify the method and amount of demolitions, they learned that there was no doctrine for this type of operation. Basing their answer on demolitions for quarrying operations, school personnel suggested boreholes as the preferred technique. However, it was not possible to drill boreholes, and explosive boreholes were not an option because of the possibility of a cave-in when reentering the cave after demolitions had been executed inside. The school personnel concurred with the platoon's assessment of the situation.
Executing the Mission
After coordinating with EOD, security, and medical-evacuation personnel, the platoon was ready to execute the mission. Because of the route conditions, Class V materials had to be shuttled to the site via a cargo HMMWV. Once the platoon reached the cave, it reestablished security, cleared and marked a lane to the entrance of the cave, and cleared a space for preparing the demolitions.
One platoon member and a soldier from the EOD team entered the cave to look for booby traps and caches. Since the cave surfaces were solid rock, there was no place to bury or camouflage booby traps, so the soldiers could visually clear the cave by using a flashlight. Moving deliberately through the cave, the two soldiers scanned all sides for anything unusual before proceeding. The clearing operation took approximately 30 minutes, and no booby traps or caches were found.
Thirty-seven cases of C4 explosives were shuttled up to the site along with the Class IV materials. To enable the charges to be placed against the sides and ceiling of the cave, platforms were constructed which would allow proper contact between the explosives and the cave surface. Figure 2 shows the placement of the charges. In addition, a crawl space was created where sappers could prime the charges once they had all been placed.
To obtain a counterforce effect, all charges had to be simultaneously detonated, so an interesting problem was posed. Due to the confinement of the cave and the amount of charges, a dual-fired system consisting of British junctions was not a feasible solution. A modernized demolition initiator (MDI) would have to be used to ensure a simultaneous detonation. However, it had to be verified that all the M11 shock tubes used to prime the explosives were the same length from the charges to the shock-tube consolidation point, care had to be taken to not rupture the shock tubes in the confined and rocky environment, and accountability of M11 shock tubes had to be maintained to ensure the integrity of the two firing systems.
The MDI system worked very well. Two M11 high-strength blasting caps and shock tubes were used to prime each charge. An M11 from each charge was run to a central location, which ensured that all shock-tube lengths were equal. At that point, two M9 bunch blocks per firing system were used to consolidate the M11s, and two additional M11s were run out of the cave and tied into two series of M13 low-strength blasting caps with 1,000 feet of shock tube. This firing system would provide the necessary redundancy and ensure simultaneous detonation.
The demolition was executed and the desired effect achieved--the entrance to the cave was sealed by a massive amount of material, and the cave collapsed. This was evident by a depression in the hillside that extended along the route of the cave.
During this operation, the platoon learned demolition calculations and theory for cave and tunnel demolitions. It also learned the importance of continuing to maintain proficiency in wartime, individual engineer-specific tasks. Although the calculations worked in this case, a more detailed study would be required for developing doctrine on this subject. In addition, entering and clearing the cave was an engineer job that had not been performed recently. However, with continued battle-focused training, these skills will not be forgotten.
First Lieutenant Swilley, who led 1st Platoon, Alpha Company, 16th Engineer Battalion, during this operation, is the training officer for the battalion. He holds a bachelor's in civil engineering from Louisiana State University and is a graduate of the Engineer Officer Basic Course.
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|Publication:||Engineer: The Professional Bulletin for Army Engineers|
|Date:||Aug 1, 2001|
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