The M198 155mm howitzer is a split trail carriage-designed towed field artillery weapon. A double baffle muzzle brake and a variable length hydropneumatic recoil mechanism are features of the M198. Trail-first transport of the M198 is accomplished by suspending the cannon over a solitary set of wheels. When the cannon is in a forward position for firing and transportation, it can be rotated 180 degrees (over the trail) for storage.
The howitzer does not remain anchored while in motion; instead, it is supported by the traveling axles. In order to discharge the M198 from “limbered” (traveling configuration) status, it is necessary to have it firmly positioned. There is no provision for attaching a splinter deflector to the M198; one is not included by default. The breech is a screw-type mechanism that is operated manually. Non-fixed (projectile and propellant are distinct) ammunition is fired from the M198, which can accommodate an arbitrary number of propellant bags. The M198 possesses the ability to deliver fire support in both direct and indirect capacities.
The M198 can be externally slung by CH-47D and CH-53E heavy lift helicopters; it cannot be transported by C-5 and C-17 aircraft. However, it lacks CV-22 Osprey capability.
The traveling and launching configurations of the M198 howitzer weigh a combined 15,760 pounds, while its length in the firing configuration is 35.75 feet (compared to 40 feet in the traveling configuration and 24 feet when stowed). The cannon possesses a transverse traverse of 45 degrees and is capable of being raised by a range of 72 to -5 degrees. The M939 6×6 5-ton truck is the standard ground transport vehicle for the M198, and the cannon itself requires a crew of nine.
The sustained rate of fatigue for the M198 is four rounds per minute. Maximum range of the howitzer: 18,100 meters when standard 95-pound M107 HE and M864 DPICM projectiles are discharged; 30,000 meters when 97-pound M549 RAP rounds are discharged.
1968 marked the beginning of development for the M198 155mm towed howitzer, which was designed to supplant the M114 155mm howitzer of World War II in a lighter weight. At the Army’s Rock Island arsenal, a testbed prototype was designed and built in 1969, and discharge trials commenced in 1970. After undergoing preliminary discharge trials, the Army received two prototype M198 howitzers in 1972. Subsequent to further testing, the M198 howitzer was put into continuous production in 1978. In April 1979, the initial Army M198 unit made its operational debut.
Since their introduction into production, more than 1,600 units have been produced, with the last unit leaving Rock Island in 1992.
Although the M198 is presently operational in the United States Army and Marine Corps, it is being phased out in certain units in favor of the M777 ultra-lightweight 155mm howitzer.