The M549 is a high-explosive rocket-assisted (HERA) 155 mm howitzer round developed for use by the US military in order to add additional range to standard howitzers, with a maximum range 30.1 km (18.7 mi) from a M198 howitzer. The projectile has two distinctive pre-assembled components—the high explosive (HE) warhead and the rocket motor, making it a form of rocket-assisted projectile. The warhead is fabricated from high fragmentation steel for increased effectiveness in terms of damage caused to target and contains a bulk-filled explosive.

The M1156 Precision Guidance Kit (PGK), formerly XM1156, is a U.S. Army-designed precision guidance system to turn existing 155 mm artillery shells into smart weapons. The prime contractor was Alliant Techsystems – later merging with Orbital Sciences Corporation to form Orbital ATK, in turn being taken over by Northrop Grumman and renamed Northrop Grumman Innovation Systems – and the industry team includes Interstate Electronics Corporation. By April 2018, more than 25,000 PGKs had been produced.