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M777 Lightweight 155mm howitzer (LW155)

The Lightweight 155 (LW 155), formerly known as the Advanced Towed Cannon System (ATCAS), LW 155 will replace all US Marine Corps (USMC) cannon systems and be used as a direct support weapon. The US Army (Army) will use the system as a general support weapon in the light forces and as a direct support weapon for the Light Cavalry Regiment replacing all of the M198 155mm towed howitzers.

The lightweight 155mm howitzer (XM777) will be a great improvement over the M198 in terms of capability, due in large part to its Automated Fire Control System. The XM777's biggest drawback remains the fact that it is a towed system with the same large logistical footprint as the M198. The two largest detractors of towed artillery are the amount of lift necessary for ship to shore movement of the battery, and the difficulties of employment in an urban environment (turning radius, crew survivability, greater time and space needed to employ the gun).

The Marine Corps has a valid, approved, high priority requirement for an advanced towed lightweight 155mm howitzer that meets increased operational thresholds for mobility, survivability, deployability, and sustainability in an expeditionary environment. The Army shares this fire support requirement in the interest of its light forces. The Marine Corps (ACMC) approved a Joint Operational Requirements Document (JORD) in June 1995, and the Army approved it in September 1995. This system combines both Army and Marine Corps efforts to replace the M198 with the more responsive LW155.

The LW 155 will provide close and deep fire support and interdiction fires. It will be lightweight without sacrificing range, stability, accuracy or durability. The system is designed as a howitzer, prime mover and associated equipment. The system shall be deployable to any region and shall operate in most climatic conditions. The US Marine Corps will use the weapon as a direct support weapon, replacing all existing cannon systems. The US Army will use the LW 155 as a general support weapon in the light forces and as a direct support weapon for the Light Cavalry Regiment, replacing the M198 155mm towed howitzer.


Weight: 10,500 lbs or less
Range: 30-40 km (assisted), 22.5-30 km (unassisted)
Range Precision PE: .35% (assisted), .30% (unassisted) of range
Deflection Precision PE: 1 mil (low angle), 2 mils (high angle)
Accuracy: 200-50 meters CEP, at 25 km w/ 20 km Met separation.
Minimum Range: 3.7-2.7 km high angle
Maximum Rate of Fire: 5-8 rds/min for NLT 2 minutes
Min Elevation: 0 mils or less (300 mils for charge M119A2/M203A1)
Maximum Elevation: At least 1275 mils
Sustained Rate Of Fire: At least 2 rds/min
Emplacement Time: 3-2 minutes w/ 5 crewmen (ready to fire)
Displacement Time: 2-1 minute w/ 5 crewmen
Out Of Sector: 3200 mils left/right in 3-2 minutes w/ 5 crewmen
Chamber Temp: Sensor for misfire proc. and ROF limitations
External Lift: CH-53E & CH-47D @ high/hot (4000 ft/95oF); MV-22 & CH-53D @ low/cool (Sea Level/60oF)
Strategic Lift: 2 in C-130; LW155 w/ PM C-141B, and larger
Heavy Drop: Yes (LVAD) from C-130 and larger
Ground Mobility: NTE towing capabilities of PM; equiv. fording
Prime Mover: USMC - MTVR, Army - FMTV 5 ton
Direct Fire PH: 30-80% @ 1500 meters
Moving Target Capability: Required w/ lead/night/poor visibility enhancement

The LW 155 indirect fire maximum range shall be at least 30 (threshold) to 40 (objective) kilometers with rocket-assisted US munitions (i.e., M549A1) and 22.5 (threshold) to 30 (objective) kilometers with unassisted US munitions (i.e., M795, M825A1 or XM898) with the M203A1 propelling charge. The LW 155 high angle indirect fire minimum range firing the M107 projectile and current propelling charges shall not be greater than 3,700 (threshold) to 2,700 (objective) meters.

Bias errors cause the offset between the fall-of-shot mean point of impact (MPI) and the target. The goal of artillery is to center the MPI on the target. The LW 155 shall have a bias circular error probable (CEP) not exceeding 200 meters (threshold) to 50 meters (objective) at 25 kilometers. This is based upon a two hour MET with 20 kilometer spatial separation from the MET station to the midpoint of the trajectory, firing the M864 projectile at low angle with the maximum charge, and a target location accuracy of 10 meters.

Precision errors cause the fall-of-shot pattern. They are related to the interaction of component tolerances, such as cannon, fire control, projectile, and propellant. The LW 155 range precision probable error for low angle indirect fire shall not be greater than 0.0030 (.3 percent) of range for unassisted projectiles and 0.0035 (.35 percent) of range for assisted projectiles. Deflection probable error shall not exceed one mil at any range in low angle fire and two mils in high angle fire for both assisted and unassisted projectiles.

The maximum rate of fire for the LW 155 shall be at least five (threshold) to eight (objective) rounds per minute firing all allowable shell/charge combinations (Copperhead excluded) for not less than two minutes in low angle fire (800 mils or less).

The sustained rate of fire shall be at least two rounds per minute firing all allowable shell/charge combinations (Copperhead excluded) in low angle fire (800 mils or less) for as long as ammunition is available. As a minimum, this quantity should equal the gun section's basic combat load.

The LW 155 (a single weapon) shall be emplaced and ready to fire (weapon is laid, at least one reference point has been established, one round of ammunition is ready to be loaded, and communications with the Fire Direction Center (FDC) are established) by no more than five crewmen including the gunner and four other cannoneers in three (threshold) to two (objective) minutes or less, after the prime mover has stopped in position. Once emplaced, the LW155 (howitzer, crew, prime mover, and associated equipment) shall be loaded and prepared to immediately depart the current location, by no more than five crewmen in two (threshold) to one (objective) minute.

The LW155 is a joint acquisition program. The Marine Corps Acquisition Objective (AO) is 377 howitzers, with an Initial Operational Capability (IOC) scheduled for 2QFY02, and Full Operational Capability (FOC) during FY06. The Army's AO is 273 howitzers with an IOC planned for FY06. To ensure that the LW155 meets the needs of both Services, enhanced technologies and design features not available at Marine Corps IOC will be later incorporated through a preplanned product improvement program.

The LW155 threshold weight is 10,500 pounds. The objective weight is as light as practical without sacrificing other performance characteristics included in this document, such as range, accuracy, survivability, and reliability/durability. The system weight includes the basic weapon, optical fire control and section equipment needed to fire the weapon. Non-critical section equipment, M93/94, and radios are not included.

The LW155 Mean Rounds Between System Abort (MRBSA) shall be no less than 800 rounds (threshold) to 900 rounds (objective), to be demonstrated with an 80% confidence, when employed IAW with the LW155 Design Reference Mission Profile.

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