Staff Writer (Updated: 9/28/2016):
The M108 was a fully-armored, full track-laying vehicle that provided a self-propelled carriage for its M103 series 105mm caliber howitzer gun system. The weapon was loaded from the breech and featured a 4 rounds-per-minute rate-of-fire with range out to 11.5 kilometers (rocket-assisted projectiles could reach in excess of 15 kilometers). The gun barrel was capped by a rather unique-looking muzzle system and gave a muzzle velocity of approximately 1,550 feet per second. The M108 sported its 105mm armament within a 360-degree traversing turret emplacement set about the hull roof. A crew of five included the driver, commander, gunner and ammunition handlers. The driver resided in the hull with the remaining crew in the turret. Hatches were installed at the rear hull face and rear of the turret to allow for easier management of spent shell casings and reloading in-the-field. The track system consisted of seven double-tired road wheels to a hull side with the drive sprocket at front and track idler at rear. There were no track return rollers used. The vehicle weighed 21 tons and featured an overall length of 6.11 meters with a width of 3.15 meters and a height to turret roof of 3.28 meters. Beyond the main armament - which was largely offensive in nature - the vehicle mounted a Browning M2 12.7mm heavy machine gun for self-defense against light-armored vehicles, infantry and low-flying aircraft. Vehicles were usually stocked with several M14 semi-automatic rifles (or similar) for close-in defense by the crew as well as an M20A1B1 rocket launcher. Up to 87 x 105mm projectiles were carried aboard as was 500 x rounds of 12.7mm ammunition.
Power was served through a GMC Detroit Diesel 8V71T series turbocharged V8 2-stroke, liquid-cooled diesel engine of 425 horsepower. This supplied the frame with a top road speed of 56 kmh with an operational range out to 386 kilometers.
In practice, the M108 proved adequately mobile for a vehicle of this class, utilized primarily for direct-fire support alongside combat teams when employed with Armored Personnel Carriers, combat tanks or light tanks. Since it was adopted in the 1950s, the M108 series was available for combat service in the Vietnam War with US forces. It served throughout the conflict and was eventually phased out after the end of the American involvement in Southeast Asia - there proving to be a definitive shift to the 155mm caliber weaponry of the M109 series over the lighter 105mm weapon of the M108. As the M109 was developed along the same lines as the M108 before it - utilizing the same chassis and turret configuration - it mimicked the form and function of the preceding design - though proving much more popular and tactically valuable.
The M108 is no longer in service with US forces but was adopted by the armies of Belgium, Brazil, Spain, Taiwan, Turkey and Tunisia. The Belgian Army managed up to 90 examples into the 1980s before retiring them in full. Brazil operated some 50 units under the local designation of M108AP while Spain was handed 48 examples though since retired. Taiwan received roughly 100 M108 units. Turkey has operated the M108 under the export designation of M108T. Tunisia operates (or operated) some 48 of the type.
By and large, the M108 was directly replaced by the M109 series for those operators still requiring an SPA/SPG solution. The M109 remains in widespread use as of this writing (2013).
Production of M108 units was handled by the Cadillac Car Division of General Motors.