Also known as the XM982 Precision Guided Extended Range Artillery Projectile, the M982 Excalibur is a guided shell for 155mm howitzers, developed by the U.S. and Sweden. Development began at a U.S. Army internal laboratory, and moved to a team of Raytheon and General Dynamics, which merged with a program with Sweden's Bofors. As with the Joint Direct Attack Munition guided bomb, the projectile would use inertial guidance with additional precision from the Global Positioning System (GPS).
Howitzers that fire it include the M109 self-propelled howitzer, the lightweight towed M198, and the ultralightweight M777. It was first used in combat, in Iraq, in late 2007. Although it is more effective than unguided rounds because a single shell can do the work of several, cost is still a consideration and cost reduction engineering is underway. Current single-round costs are approximately $100,000, but the Army decided to cut procurement, in summer 2010, from 30,000, to 6,264 shells. Other alternatives are being considered, such as "near-precision" but much cheaper shells with a 30 meter circular error probability (CEP). 
Free spinning base fins stabilize the projectile, while four-axis canard fins provide steering. Range and accuracy would be extended by base bleed, as well as a glide rather than ballistic-only phase of flight. Range would extend to at least 40km, well in excess of that of the existing, base-bleed but unguided M864 shell, and far greater than the non-base-bleed M107 shell. Range depended on the barrel length of the firing howitzer. A complementary program is intended to fire a 127mm (5") shell, modified with a sabot to make it fit 155mm barrels but travel with higher speed, for ranges up to 70 km. 
CEP is less than 10 meters, allowing it to be used within 150 meters of civilians and friendly troop. 92 percent land within 6 meters, better than the planned CEP. It could engage targets that were not in a straight line with the barrel.
As opposed to the M864, the Excalibur could use a unitary explosive warhead, not only dual-purpose (i.e., against people as well as light armor) cluster submunitions that are increasingly banned. It also can carry acceptable SADARM (sense and destroy armor) cluster submunitions that are set off only by tanks.
- Matthew Cox (September 2010), "Artillery Munitions Modernization", Ground Combat Technology
- XM982 Excalibur Precision Guided Extended Range Artillery Projectile, Globalsecurity