fire. To allow the most shells to reach the target, the target has to be in range of the lowest propellant charge. Examples of guns with a rate of fire that makes them suitable for MRSI includes UK's AS-90, South Africa's Denel G6-52 (which can land six rounds simultaneously at targets at least away), Germany's Panzerhaubitze 2000 (which can land five rounds simultaneously at targets at least away), Slovakia's 155 mm SpGH ZUZANA model 2000, and K9 Thunder. The Archer project (developed by BAE-Systems Bofors in Sweden) is a 155 mm howitzer on a wheeled chassis which is claimed to be able to deliver up to six shells on target simultaneously from the same gun. The 120 mm twin barrel AMOS mortar system, joint developed by Hägglunds (Sweden) and Patria (Finland), is capable of 7 + 7 shells MRSI. The United States Crusader program (now cancelled) was slated to have MRSI capability. It is unclear how many fire control computers have the necessary capabilities. Two-round MRSI firings were a popular artillery demonstration in the 1960s, where well trained detachments could show off their skills for spectators. Air burst The destructiveness of artillery bombardments can be enhanced when some or all of the shells are set for airburst, meaning that they explode in the air above the target instead of upon impact. This can be accomplished either through time fuzes or proximity fuzes. Time fuzes use a precise timer to detonate the shell after a preset delay. This technique is tricky and slight variations in the functioning of the fuze can cause it to explode too high and be ineffective, or to strike the ground instead of exploding above it. Since December 1944 (Battle of the Bulge), proximity fuzed artillery shells have been available that take the guesswork out of this process. These employ a miniature, low powered radar transmitter in the fuze to detect the ground and explode them at a predetermined height above it. The return of the weak radar signal completes an electrical circuit in the fuze which explodes the shell. The proximity fuze itself was developed by the British to increase the effectiveness of anti-aircraft warfare. This is a very effective tactic against infantry and light vehicles, because it scatters the fragmentation of the shell over a larger area and prevents it from being blocked by terrain or entrenchments that do not include some form of robust