In early April Ukraine requested 400 artillery systems from friendly, mostly NATO, countries. This included 100 MLRS (multiple launch rocket systems) and 300 howitzers, preferably self-propelled. By early May NATO nations pledged or delivered over half that number and considered sending more by taking them from their reserve or even active-duty units. NATO countries are eager to supply their artillery systems because Ukraine has developed novel and very effective tactics and new fire control tech that made Ukrainian artillery much more effective, and less vulnerable, than Russian artillery. Because of this Ukrainian artillery does not have to operate as batteries (six howitzers) or battalions (three batteries) as the Russians do. Most Ukrainian artillery operates as individual vehicles or towed systems that can halt, fire one or two shells at a designated target and be moving again in a minute or so. Since 2014 the Ukrainians have developed a lot of new tech and tactics, especially for artillery, which proved itself once the Russians invaded and provided more targets. The effectiveness of Ukrainian counterbattery (firing at enemy artillery) is one reason why Russian artillery is now mainly used against cities and civilians, which have no counterbattery capability.
So far France has sent twelve Caesar vehicles. This is the lightest of the truck-mounted 155mm howitzers, weighing 18 tons. Other nations have built heavier (20-30 ton) systems, usually on a 6x6 or 8x8 heavy truck chassis. The Ukrainian made 2S22 truck-mounted 155mm system was ready for service in 2018 but the Ukrainian military did not adopt it until early 2022. Obtaining more is difficult because the Kharkiv Tractor Plant producing it is in Kharkiv, a city subjected to Russian artillery fire in the first week of the invasion. The Kharkiv factory was heavily damaged but in March it was revealed that Kharkiv Tractor Plant operations were being restarted in Romania using equipment salvaged from the Kharkiv plant by employees. It will be a while before more 2S22 vehicles are produced.
Other NATO nations have sent tracked self-propelled howitzers as well as towed M777s , a British design that is, at four tons, is the lightest 155mm towed howitzer ever fielded. M777 Fire control is handled by a computerized system that allows faster response time and more accurate shooting. Users have found M777 accurate and reliable. U.S. Marines as well as Canadian British troops used the M777 in Afghanistan.
So far Ukraine has only received about half the MLRS systems requested, all of them 122mm MLRS systems from Poland and the Czech Republic. What Ukraine wants from the Americans is the truck mounted MLRS (HIMARS) rocket launcher system (preferably) or even the original tracked MLRS. HIMARS carries only one, six MLRS rocket, container instead of two in the original MLRS vehicle. The 12-ton truck can fit into a C-130 transport, unlike the 22-ton tracked MLRS, and is much cheaper to operate. The first HIMARS entered service in 2005, about a year after GPS guided rockets did. The 309 kg (680-pound) GMLRS (guided multiple launch rocket system) missile is a GPS guided 227mm rocket that entered service in 2004 and by 2006 it was the only 227mm rocket used. GMLRS was designed to have a range of 70 kilometers and the ability to land within meters of its intended target, at any range. This is possible because it uses GPS (plus a back-up INS/inertial guidance system) to find its target. In 2008 the army tested GMLRS at max range (about 85 kilometers) and found that it worked fine. This enables one MLRS/HIMARS vehicle to provide support over a frontage of 170 kilometers, or, in places like Afghanistan, where the fighting can be anywhere, an area of over 20,000 square kilometers. This is a huge footprint for a single weapon (an individual MLRS/HIMARS vehicle), and fundamentally changes the way you deploy artillery in combat. By way of comparison, unguided 155mm shells have a max range of 40 kilometers and the Excalibur (PS guided 155mm shell has a max range of 37 kilometers. Another edge GMLRS has is the HIMARS vehicle. These cost about $5 million each. Over 400 HIMARS have been built so far. About 1,300 of the original tracked MLRS were produced between 1980 and 2003 and most are still in service or held in reserve. The United States Army has hundreds in reserve.
Ukraine is willing to demonstrate what all these artillery systems are really capable of.