M109A4 155mm SP Howitzer
The M109A4 is a M109A2/A3 improvements include the addition of Nuclear, Biological, and Chemical/ Reliability, Availability, and Maintainability (NBC/RAM) product improvement kits. The driver and cannoneer no. 2 have an air purifier and two heaters mounted in the hull. An air purifier and four heaters are mounted in the cab for the rest of the crew. NBC Mission Oriented Protective Posture (MOPP) gear is stored in the new cannoneer seats and stowage boxes.
The traversing mechanism is operates with a hydraulic clutch in the M109A4 instead of operating with an electric clutch as in the traversing mechanism in the M109A2/A3 howitzers. A clutch valve with an override valve provides for power traversing in the event of an electrical failure to the clutch valve solenoid. The M109A4 has two hydraulic filters mounted outside of the power pack. The M109A2/A3s have one internal hydraulic power pack filter.
The M109A4 has a combat override switch to allow for emergency starting. The slave start receptacle has been moved from the battery compartment to the driver's compartment. The M109A2/A3 100 amp alternator has been replaced by a 180 amp alternator. Crew compartment subfloor drains have been added to provide for the drainage of DS2 used in the NBC decontamination process and provide for the drainage of excess water.
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