The SP-122 was an American-designed and developed weapon exclusively for service with the Egyptian Army. Work was carried out by BMY Combat Systems (now United Defense LP) and served in the Self-Propelled Howitzer (SPH) role, mounting a 122mm caliber main gun within a fixed superstructure atop the American M109A2 SPH tracked chassis. Instead of adopting the 155mm-armed M109 outright, it was decided to install the Soviet D-30 series guns to the vehicle line, a weapon already locally manufactured under license in Egypt. As such, there was a readily available stock of munitions for the gun which proved logistically sound for long-term service. In all, 124 of the type were completed and delivered in three production batches up through 2000.
The vehicle's profile remained largely faithful to the M109 with the major exception being its smaller-caliber main gun and fixed superstructure. Without a turret - which simplified manufacture and maintenance - the vehicle had to turn to face the designated target area once outside of the traversal range of the gun mounting hardware. Traversal of the gun system was limited to 30-degrees from center while elevation showcased a span of -5 to +70 degrees.
As a howitzer-based battlefield system, the SP-122 fired its projectiles indirectly at a target location, not requiring line-of-sight as a field gun would. Range of the gun, through use of conventional projectiles, was just over 15 kilometers though Rocket-Assisted Projectiles (RAPs)increased this range slightly further. A multi-baffled muzzle brake was fitted over the business end of the gun to help content with the ferocious recoil effects of such a large-caliber weapon (in addition to the integral recoil mechanism already fitted to the gun near the breech). A barrel clamp was affixed to the front end of the glacis plate which locked the main gun in place during travel. A machine gun could be mounted to the turret roof for local air defense. The crew numbered five and included a driver in the hull front-left with the commander, gunner and two loaders in the superstructure. 85 x 122mm projectiles were carried with 500 x 12.7mm rounds of ammunition.
Power was served through a Detroit Diesel 8V-71T turbocharged, 8-cylinder, diesel-fueled engine developing 405 horsepower and fitted in the hull front-right. With its track-over-wheel arrangement and torsion bar suspension system, the SP-122 provided a maximum road speed of 40 miles per hour with operational range of 215 miles. The running gear included seven rubber-tired road wheels with a front-mounted drive sprocket and rear-mounted track idler. No track return rollers were used.
Dimensions of the SP-122 included an overall length of 6.9 meters with a width of 3.15 meters and a height of 2.8 meters. Combat weight was listed at 23,180 kilograms.