The 155-mm howitzer-equipped M109 serves as the primary self-propelled artillery support for U.S. Army divisions and is extensively utilized. It is a sizable tracked vehicle featuring a bustle and a turret that are both completely traversable. Initial iterations featured a 23-caliber, short barrel. The barrel of later models, such as the M109A6 Paladin, is 39 caliber.

There are six crew members on the M109: the commander, gunner, driver, and three ammunition members. All-welded aluminum armor adorns the superstructure, providing protection from small-arms fire and shell splinters.

Placing the pilot in the front left corner of the hull, the turret is situated in the rear, and the powerpack is oriented to the right. A single-piece hatch cover that opens to the left conceals three M45 day periscopes positioned in front of the operator. These can be protected from harm by enveloping them in thin metal flaps. A passive night-vision periscope may be utilized in lieu of one of the day periscopes.

A Detroit Diesel Model 8V-71T engine is mated to a cross-drive Allison Transmission XTG-411-4A gearbox.

The rear of the hull features an all-welded aluminum armor turret with twin entrances and a square hatch on each side that provides access to the rear. Situated on the right side of the turret, the commander is equipped with an M27 day periscope, a single-piece entrance cover that opens to the rear, and a cupola with a 360-degree traversal capability. A pintle-mounted,.50-caliber M2 heavy-barrel machine gun is positioned in front of the cupola.

The gunner is situated on the left side of the turret and is equipped with a right-opening square single-piece aperture cover. Provisioned at the rear of the turret are twin apertures for resupply of ammunition. A substantial spade is affixed to the hull’s rear, positioned on either side of the hull door. Prior to launching, it requires manual descent to the ground. Typically, they are only utilized during the discharge of high charges.

Seven dual-tired road wheels comprise the torsion bar suspension on each side; the drive sprocket is positioned in front, while the idler is situated at the rear. No track-return rollers are present. Single-pin, center-guide tracks featuring replaceable rubber cushions are utilized.

Although night-vision apparatus is installed on the M109, it lacks protection against nuclear, biological, and chemical (NBC) warfare. An amphibious system comprised of nine air bags, four on each side of the hull and one in the front, is available for installation on the vehicle. The vehicle inflates the sacks and subsequently utilizes its tracks to traverse rivers at an accelerated rate of 4 mph (6 km/h).

A 155-mm M126 artillery mounted on an M127 with a fume extractor and a substantial muzzle brake constitutes the primary armament. The recoil mechanism is hydropneumatic, while the breech block features a Welin-step thread design. For emergency use, the gun depression and elevation and turret traverse are hydraulic and controlled manually.

The fire-control apparatus consists of a 10-degree field of view, 4-x magnification elbow telescope M118C designated for direct fire; a panoramic telescope M117 designed for indirect fire; and a gunner’s quadrant M1A1 telescope.

The forthcoming overhaul of the M109 Paladin self-propelled howitzer, which debuted in 1963 and has undergone significant enhancements over the last four decades, is at present a comprehensive undertaking. By utilizing numerous Bradley Fighting Vehicle components, the M109 PIM modification facilitates greater compatibility with other Army vehicle systems, thereby optimizing production costs, inventory of spare parts, and maintenance personnel. Furthermore, this approach prevents the obsolescence of components.

The M109A6 Paladin is substantially improved through the PIM modernization initiative, which entails the reacquisition of power, space, and weight, as well as cooling. Although the cannon of the self-propelled howitzer will remain unaltered, the PIM will feature an enhanced electric ramming system and a brand-new chassis, engine, transmission, suspension, and steering system.