A rocket-assisted projectile (RAP) is a cannon, howitzer, mortar, or recoilless rifle round incorporating a rocket motor for independent propulsion. This gives the projectile greater speed and range than a non-assisted ballistic shell, which is propelled only by the gun's exploding charge. Some forms of rocket-assisted projectiles can be outfitted with a laser guide for greater accuracy.
The German Sturmtiger (1944) used a 380 mm (14.9-inch) Rocket Propelled Round as its main projectile. These rounds were high explosive shells or shaped charges with a maximum range of 6km (04miles). The gun first accelerated the projectile to 45 m/s (150 ft/s), the 40 kg (88 lb) rocket charge then boosted this to about 250 m/s (820 ft/s).
Also the German Krupp K5 railway gun of World War 2 used rocket-assisted projectiles in the later stages of the war, although it also used conventional artillery projectiles.
The North Korean M-1978 / M-1989 Koksan 170 mm (6.7-inch) self-propelled gun can use rocket-assisted projectiles to achieve a range of around 60km (40miles); at one time this was the world's longest-range tube field artillery piece.[1]
When NATO standards required member armies to have corps-level artillery that could fire to a minimum range of 30km (20miles), nearly all member nations solved the problem with RAP rounds in their 155 mm (6.1-inch) artillery. The Belgian Army was the only NATO member army that did not require RAP, reaching the required range with a conventional round.
The XM1113 RAP round replaced the M549A1 RAP round for the M777 howitzer and other 155 mm (6.1-inch) artillery after 2016. The new round had a range of 39km (24miles) instead of the 30km (20miles) NATO standard. As of 2016, the XM1113 was scheduled for Limited Rate Initial Production in fiscal year 2022.[2]