M109 SPA 155mm Self-Propelled Artillery
Still going strong - the M109 Self-Propelled Artillery system debuted in the Vietnam War and has continued a useful service life in the new millennium.
Authored By Staff Writer; Content ©www.MilitaryFactory.com
The155mm-armed M109 Self-Propelled Howitzer (SPH) was developed concurrently with the 105mm-armed M108 SPH. Both shared the same hull superstructure and turret design and were differentiated primarily by their choice of armament. The M108 was eventually given up in the long run in favor of the more powerful M109 offering to which the M109 has since enjoyed an exceedingly long operational service life thanks, in part, to a strong design and modernization programs. Its endorsement by the U.S. Army and USMC - and its subsequent combat use during the Vietnam War (1955-1975) - led to its wide acceptance by other global land armies aligned with the United States. Production of both the M108 and M109 systems began in 1962 though manufacture of the M108 ended the following year. The M109 continued in production up until 1969 and was manufactured under several related brand labels: General Motors (Cadillac Motor Car Division), General Motors (Allison), and Chrysler Corporation - interestingly all from the same Cleveland facility. Bowen-McLaughlin-York added additional production in 1974 to meet new demand.
Initial M109 production vehicles were fitted with the T255E4 short-barreled main gun which proved effective but led to excessive wear-and-tear due to the propellant charges in use. This prompted a slight revision of the design which introduced a longer-barreled gun tube in the XM185. The existing M109 fleet was then converted to the new M109A1 standard beginning in 1972 with operational levels reached the following year. During 1974, more M109A1s were built to strengthen existing stocks, these by Bowen-McLaughlin-York, and designated M109A1B.
As completed, the M109 was a conventional SPA form by modern standards. It fitted its powerpack at front-right with the driver at front-left in the forward hull. The turret was placed over the rear section of the vehicle with the large main gun fitted into the forward panel. A cupola was afforded to the commander's position to which a 0.50 or 0.30 caliber machine gun could be installed for air/local defense. The vehicle sat atop a track-and-wheel arrangement which included seven double-tired road wheels to a hull side. The drive sprocket was at front with the track idler at rear while no track return rollers were used. A small door at the rear of the hull allowed for crew entry exit as did side panels, roof hatches and a hatch over the driver's compartment. Main guns featured massive muzzle brakes and were clamped to the hull when traveling. Despite the 155mm caliber, there proved little barrel overhang. The operating crew numbered six - driver, commander, two gunners and two loaders. Turret traversal was a full 360-degrees.
After a period of in-the-field use, more revisions were ordered which included a larger turret bustle which accepted more onboard ammunition storage. New gun mounting hardware was also installed and the floatation equipment seen in original production models was dropped. With these changes in place, the U.S. Army adopted the M109A2 standard and 823 x A2 models followed from 1976 into 1985. Existing M109A1 and M109A1B models were all modified to the A2-standard and these became M109A3.