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<center>Sniper and anyone that's interested:
This an excerpt from an army manual on MOUT operations. This one section I posted describes the weapon effects for 120mm ammunition.</center>
7-11. TANK CANNON
The powerful, high-velocity cannon mounted on the M1-series tanks provides the infantryman heavy direct-fire support. Although the infantry assumes the lead role during combat in urban areas, tanks and infantry work as a close team. Tanks move down streets, after the infantry has cleared them of any suspected ATGM positions, and, in turn, support the infantry with fire. The tank is one of the most effective weapons for heavy fire against structures. The primary role of the tank cannon during urban combat is to provide heavy direct-fire against buildings and strongpoints that are identified as targets by the infantry. The wall and fortification breaching effects of the 105-mm and 120-mm tank cannon are major assets to infantrymen fighting in urban areas.
a. Obliquity. Tank cannons produce their best urban target effects when fired perpendicular to the hard surface (zero obliquity). During urban combat, however, finding a covered firing position that permits low-obliquity firing is unlikely. Most shots strike the target at an angle that would normally reduce penetration. With a tank cannon, a HEAT multipurpose round is the item of choice against urban targets; the size of the hole is reduced by approximately 1/3 when the firing angle is 45 degrees.
b. Ammunition. Armor-piercing, fin-stabilized, discarding sabot (APFSDS) rounds work best against armored vehicles. Other types of ammunition are carried that are more effective against masonry targets and other urban structures. The 105-mm cannon has HEAT, HEP, and WP rounds in addition to APFSDS. The 120-mm cannon has an effective high-explosive, antitank, multipurpose (HEAT-MP) round, which also has capability against helicopters. The 120-mm tank can also carry a high-explosive, concrete-obstacle reduction cartridge that has rubbling capability.
c. Characteristics. Both 105-mm and 120-mm tank cannons have two specific characteristics that affect their employment in urban areas: limited elevation and depression, and short arming ranges. In addition, the M1 and M1A1/M1A2 tanks have another characteristic not involved with its cannon but affecting infantrymen working with it—extremely hot turbine exhaust.
(1) The M1 and M1A1/M1A2 tanks can elevate their cannon +20 degrees and depress it -10 degrees. The lower depression limit creates a 35-foot (10.8-meter) dead space around a tank. On a 16-meter-wide street (common in Europe) this dead space extends to the buildings on each side (Figure 7-15). Similarly, there is a zone overhead in which the tank cannot fire (Figure 7-16). This dead space offers ideal locations for short-range antiarmor weapons and allows hidden enemy gunners to fire at the tank when the tank cannot fire back. It also exposes the tank's most vulnerable areas: the flanks, rear, and top. Infantrymen must move ahead, alongside, and to the rear of tanks to provide close protection. The extreme heat produced immediately to the rear of the M1-series tanks prevents dismounted infantry from following closely, but protection from small-arms fire and fragments is still provided by the tank's bulk and armor. The M1-series tanks also have a blind spot caused by the 0-degree of depression available over part of the back deck. To engage any target in this area, the tank must pivot to convert the rear target to a flank target.
Figure 7-15. Tank cannon dead space at street level.
Figure 7-16. Tank cannon dead space above street level.
(2) HEAT type rounds arm within 15 to 30 meters from the gun muzzle. On a 16-meter-wide street, HEAT type ammunition does not arm quickly enough to engage a structure directly perpendicular to the direction of travel. HEAT type rounds fired at structures less than 30 meters from the muzzle will provide some of the desired effects, particularly if the desired effect is casualties inside the building. However, the effectiveness of unarmed HEAT type rounds will be unpredictable and highly variable. These arming distances allow the tank to engage targets from short ranges. The armor of the tank protects the crew from both the blowback effects of the round and enemy return fire. The APFSDS round does not need to arm and, therefore, can be fired at almost any range. The discarding portions of tank rounds can be lethal to exposed infantry forward and to the side of the tank. Additionally, HEAT rounds have an infrequent early burst occurrence. Therefore, exposed infantry should not be forward of a firing tank (60-degree frontal arc).
d. Target Effects. High-explosive, antitank rounds are most effective against masonry walls. The APFSDS round can penetrate deeply into a structure but does not create as large a hole or displace as much spall behind the target. In contrast to lighter HEAT rounds, tank HEAT rounds are large enough to displace enough spall to inflict casualties inside a building. One HEAT round normally creates a breach hole in all but the thickest masonry construction—a single round demolishes brick veneer and wood frame construction. Even the 120-mm HEAT round cannot cut all the reinforcing rods, which are usually left in place, often hindering entry through the breach hole (Figure 7-17). The 105-mm HEP round cuts the reinforcing rods and leaves a 20-inch hole.
Figure 7-17. Tank HEAT round effects on reinforced concrete walls.
e. Employment. Tank-heavy forces could be at a severe disadvantage during urban combat, but a few tanks working with the infantry can be very effective, especially if they work well together at the small-unit level. Tank, infantry, and engineer task forces are normally formed to attack a fortified area. Individual tanks or pairs of tanks can work together with rifle squads or platoons.
(1) Tanks need infantry on the ground to provide security in urban areas and to designate targets. Against targets protected by structures, tanks should be escorted forward to the most covered location that provides a clear shot. On-the-spot instructions by the infantry unit leader ensure the tank's fire is accurate and its exposure is limited.
(2) When the tank main gun fires, it creates a large fireball and smoke cloud. In the confines of an urban area, dirt and masonry dust are also picked up and add to this cloud. The smoke and dust of the explosion further obscure the target. Depending on local conditions, this obscuration could last as long as two or three minutes. Infantry can use this period to reposition or advance unseen by the enemy. Caution must be exercised because the enemy might also move.
(3) Tank cannons create an overpressure and noise hazard to exposed infantrymen. All dismounted troops working near tanks should wear their Kevlar helmet and protective vest, as well as ballistic eye protection. If possible, they should also wear earplugs and avoid the tank's frontal 60-degree arc during firing.
(4) Tanks are equipped with powerful thermal sights that can be used to detect enemy personnel and weapons hidden in shadows and behind openings. Dust, fires, and thick smoke significantly degrade these sights.
(5) Tanks have turret-mounted grenade launchers that project screening smoke grenades. The grenades use a bursting charge and burning red phosphorous particles to create this screen. Burning particles can easily start uncontrolled fires and are hazardous to dismounted infantry near the tank. The tank commander and the infantry small-unit leader must coordinate when and under what conditions these launchers can be used. Grenade launchers are a useful feature to protect the tank but can cause significant problems if unwisely employed.
(6) The tank's size and armor can provide dismounted infantry cover from direct-fire weapons and fragments. With coordination, tanks can provide moving cover for infantrymen as they advance across small open areas. However, enemy fire striking a tank but not penetrating is a major threat to nearby infantry. Fragmentation that is generated by antitank rounds and ricochets off tank armor have historically been a prime cause of infantry casualties while working with tanks in urban areas.
(7) Some tanks are equipped with dozer blades that can be used to remove rubble barriers, breach obstacles, or seal exits under fire.
f. Multipurpose Antitank (MPAT) Round Target Effects. The MPAT round can be very effective during UO. Different MPAT effects are described below.
(1) Heavy Armor. Because of a relatively small explosive warhead, MPAT effectiveness against heavy armor (tanks) is limited to attacks from the side and rear. Mobility kills of heavy armor can be achieved when fired at from these orientations (especially if tracks and or road wheels are struck); however, the vehicle armament is likely to remain operational.
(2) Light Armored Vehicles (LAVs). The heavy nose of the MPAT projectile makes it extremely effective against LAVs, such as the BMP. Vehicle kills can be achieved with an impact on varying locations on the hull or (if so equipped) the turret. Mobility kills can be achieved if the wheels or tracks are struck, and it is likely that a road wheel or track impact will also produce penetration of the hull structure. MPAT is effective when it impacts targets from perpendicular to highly oblique, but will function with a reduced reliability when striking excessively oblique surfaces (nearing that of a graze impact).
(3) Bunkers. The heavy nose of the MPAT projectile makes it extremely effective against earthen, timber, and or sandbag bunkers with the projectile "burying" itself into the bunker structure before warhead detonation. When this occurs, the projectile detonation produces not only lethal effects to personnel within, but a highly-destructive effect to the bunker structure itself.
(4) Buildings. MPAT is effective against buildings with wooden walls over 1 inch thick. Impact against a thinner wall structure (plywood sheathing without striking supporting members) may produce only a small hole as the projectile passes through the wall without detonating. Impact against a supporting structure (roof rafter, wall stud) causes detonation of the warhead and a subsequent hole and lethal fragmentation effects to personnel located inside. Impact against concrete walls yield holes of about 24 inches in diameter, but reinforcing bars embedded within the concrete are not likely to be cleared from the hole, unless struck directly.
(5) Helicopters. MPAT, when switched to the "A" or "air" mode, is effective against attack helicopters because of its proximity switch, which can produce mission abort kills without actually impacting the aircraft. The design of the proximity switch is such that if the projectile (set in the "A" mode) is fired against a helicopter, and is on a direct impact flight path, the projectile warhead will not function in the proximity mode, but will be detonated when the projectile strikes the target. If the projectile, however, strikes lightly armored parts of the structure (such as windows or the aluminum skin of the aircraft), it is likely to pass directly through the aircraft without detonating. Impact with heavier structures, such as the engine or transmission components, will cause detonation of the warhead.
(6) Concrete Obstacles (XM908 OR-T Projectile). The OR-T projectile, because of its steel nose, is effective against large concrete obstacles. This effectiveness comes from the projectile's striking the face of the obstacle and penetrating several inches before the warhead is detonated. This penetration fractures the concrete obstacle from within, breaking it into smaller blocks, which can be cleared with an ACE. A concrete block 6 feet in diameter and 6 feet long is broken up into rubble, which can be cleared by a tank equipped with a bulldozer blade.
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