In the end of 1940's the US Army began to work on replacing self-propelled howitzers in their inventory with newer and better designs. During the World War II self-propelled 105mm howitzers utilized modified tank chassis - M3 tank in case of the M7 Priest howitzer and M24 Chaffee tank in case of the M37 HMC. Towards the end of WWII the chassis of the M24 Chafee was lengthened to mount a 155mm howitzer - this vehicle was designated M41 HMC. After WWII M41 Walker Bulldog replaced M24 Chaffee and so it seemed natural to use the M41 tank chassis to build the next generation of self-propelled howitzers - these were the 105mm M52 HMC and 155mm M44 HMC. The chassis of M41 Walker Bulldog allowed for a quick design process of the new vehicles, but it also limited their capability - for example while it was possible to mount a 105mm in a rotary cab/turret, the 155mm howitzer had to be mounted in an open casemate, because of the limitations imposed by the chassis. Unfortunately the M44 and M52 were not successful designs and very soon the Army started to work on replacing them with even more modern designs. In order to do this it was decided to design an all new chassis and in April of 1953 work started on the T195 110mm self-propelled howitzer and T196 156mm self-propelled howitzer. Soon thereafter new, exotic howitzer calibres were dropped in favor of the more traditional 105mm and 155mm.
The designers of the new howitzers anticipated that the conditions of the late XX century battlefield would include, among other factors, also increase in the availability of artillery radars - meaning quicker and more accurate counter-battery fire has to be expected - that in turn necessitating better protection for the howitzer crews and better mobility to relocate to a new firing position faster. Better protection was also necessary to fight under NBC (Nuclear, Biological and Chemical) threat conditions. Global character of the cold war put more emphasis on lowering the mass of the new vehicles to make them air transportable. Diesel engines were considered as power source for the new designs to increase their range and reduce their vulnerability to fuel fire. The future self-propelled howitzers were also to be equipped with flotation gear allowing them to cross water obstacles swimming.
The planning phase of the project ended in October 1956 and the building of the prototypes begun. T196 was completed in March 1959, half a year later than the T195, which was a simpler vehicle, not having the recoil spades among other equipment items - the lighter weapon didn't require them. In 1960 prototypes modified by installing a diesel engine in them started being tested - the designations changed to T195E1 and T196E1. After solving several problems - among others with the suspension and chassis - the development of the prototypes was done in December 1961. Production of the new vehicles started in late 1962 while testing continued and finally they were accepted by the US Army as M108 (105 mm self-propelled howitzer) and M109 (155 mm self-propelled howitzer) in July 1963.
Introduction of the new vehicles was a technological breakthrough in self-propelled artillery. The new chassis designed especially for that application had many advantages over modified tank chassis - the most important being the large diameter turret ring providing lots of space for the weapon, it's crew and various equipment - that in turn making the vehicles easy to modify and improve. Very soon export customers started placing orders - most of them from Germany with 609 vehicles ordered.
Although the M108s and M109s were designed for a high intensity conflict in Western Europe, they were never used this way. Instead their combat debut happened in Vietnam. Here, the demand for self-propelled artillery was not very big - towed guns moved by helicopter doing most artillery jobs - but the M108s and M109s were sent anyhow and the use for them was soon found - for example as support for armored cavalry units or in fire bases where the "360 degrees" capability was needed - and the new vehicles naturally provided it. In Vietnam self-propelled howitzers usually fired from reinforced, dug in positions in fire bases and not in typical self-propelled role.
My model of the M109 self-propelled howitzer shows a vehicle from the 1st Battallion, 84th Field Artillery Regiment. This Regiment fought as part of the 9th Infantry Division in the Mekong Delta region. The model shows the vehicle as it appeared in 1968. There is not much stowage on the vehicle as the stowage usually was stored in the fire base bunkers, and on the move they were carried on the ammo carrier (M548 mover) or on an M101 trailer towed by the howitzer. Thus the model shows a vehicle on a short move between positions inside the fire base.
|Length (without gun):||6114 mm|
|Length (over gun):||6614 mm|
|Service weight:||23800 kg|
|Main armament:||M126 155 mm howitzer (M127 mount in cab)|
|Auxiliary armament:||12,7 mm M2HB machine gun|
|Armor hull:||32 mm - aluminum plate|
|Armor cab:||32 mm - aluminum plate|
|Propulsion:||General Motors 8V71T; 8 cylinder, 2 cycle, vee, supercharged diesel|
|Power (gross/net):||298 kW / 254 kW @ 2300 rpm|
|Torque:||1195 Nm @ 1600 rpm / 1308 Nm @ 1700 rpm|
|Fuel capacity:||511 L|
|Transmission:||Allison XTG-411-2A, 4 ranges forward, 2 reverse|
|Fording:||Swims with flotation gear|
|Trench crossing:||1,8 m|
|Vertical obstacle:||0,53 m|