Versions of the M109 fire one of two artillery shells.
In the 1960s, the U.S. military developed the M109 howitzer, a mobile artillery piece used for ground support operations. The military have produced several variants of the M109 since the 1963 original, including the M1905A5 and the M109A6 (1993), also known as the Paladin. These models incorporated changes to the crew, engine and weapons systems. Paladin models remain in service today, recently seeing action in Iraq.
An M109 draws power from one of two turbocharged diesel, two-stroke, eight-cylinder engines that sit just to the right of the driver. The engine in the original M109 produced 405 horsepower at 2,300 rpm. Engines in the Model M109A5 and later variants, including the Paladin delivered 440 horsepower at 2,300 rpm. The M109 engine transfers power via a seven-gear transmission.
An M109 could attain a top speed of 35 mph on road, and 12 mph when driving over terrain. It included a 135 gallon gas tank that gave it a maximum range of 217 miles. The engine in an M109A5 and later variants increased these speeds to 38 and 17 mph, respectively. These howitzers can climb graded terrain up to a 60-degree angle, cross a trench with a 6-foot depth and scale a wall 1.75 feet tall. These vehicles could cross waterways with a depth up to 3.5 feet. Operators could install an amphibious kit to the M109, which used air bags to cross rivers or water of greater depths.
Each variant of the M109 until the M109A5 included a 135 gallon fuel tank that gave it a range of 217 miles. The increased speed and power output of the M109A5 and Paladin’s engine, coupled with a 133 gallon tank, reduced the range to 186 miles.
The original M109 required a six-person crew for full operation, which the M109A6 Paladin variant cut down to four. This original crew included a driver, commander, gunner and assistant gunner to aim the howitzer’s cannon up and down and left and right, respectively, and a two-person reloading team. A Paladin’s computerized weapon system upgrade removed the need for one of the gunners and one of the reloading team members.
All variants of the M109 featured a belt-fed .50-caliber machine gun and 500 round ammo box fitted to the top of the turret. Every variant of the M109 fired a 155mm shell through its cannon; original models used .39-caliber rounds of this length, while the M109A2 and later versions fired a .23-caliber round.
Each 155 mm round weighs 98 pounds; the two-man reloading team needed to unscrew the breech (the cap covering the interior end of the cannon) to load each round after firing. This configuration gave the M109 a maximum fire rate of four rounds per minute for up to three minutes. A crew could fire one round per minute for up to one hour, with the lower fire rate permitting the cannon to cool down sufficiently in between each round.
The original M109 used a short-barrel cannon with a length of 238 inches to launch artillery; improvements to each model increased this barrel length to give the M109 greater range. An original M109 could hit targets up to 14,600 meters away; models that fired the .23-caliber rounds could ultimately strike targets from a distance of 30,000 meters.