Multi-Barrel Rocket Launchers, also called Multiple Launch Rocket Systems have existed for decades. The famous Soviet Katyushas were used extensively in WW2 and the Soviet/Russian Grad and Smerch are direct descendents of it. These systems are used to mow down enemy defenses with large scale barrages hoping to hit targets with inaccurate rockets. They aim to trade lots of cheap rockets for accuracy and hence mass attacks facilitate destruction of the entire general area being targetted.
For other articles on tanks/ships brought to the lime-light by the 2022 Russo-Ukrainian war, please see below.
Analogy 1, if Smerch and Grad are Nokia 3310, old but reliable, HIMARS is iPhone 14 Pro Max (as of September 2022). They try to the reduce number of rockets launched to hit the targets with fewer GPS guided rockets. The biggest advantage is that they can be used in cities to reduce collateral damage. While Grad and Smerch act like a massive sledge hammer, HIMARS is a scalpel and can hit a particular area of a particular building. Hence HIMARS is closer to GPS guided close air support than regular artillery, which apart from rounds like Excalibur and Krasnopol are dumb rounds like Grad and Smerch.
Modernized 300 mm BM-30 Smerch
So, what is HIMARS? HIMARS stands for High Mobility Artillery Rocket System, while being named an Artillery system, in terms of accuracy and capabilities it is closer to air launched munitions. The term HIMARS is used for the truck mounted M142 system that just needs a protect 6×6 chassis to function. It was originally derived from the M270. The M270 first showed up in the 1980s as a tracked platform with a protected 2×6 missile module. The missiles used initially were dumb rounds but currently fire the M30/M31 smart GPS guided solid fueled rockets.
M270 in action
The M142 takes 1×6 missile module and mounts it on a protected 6×6 wheeled platform. It trades offroad mobility for onroad mobility and higher top speed. The area it gains the most in is air mobility. M142s can be moved using C-130s and thus can be delivered very close to the frontlines if needed. This makes the M142 an excellent shoot and scoot platform. Both the M270 and M142 can swap their 6 missile modules for MGM-140 single missile module (so M270 can carry two ATACMS and M142 carries a single ATACMS). The MGM-140, more commonly known as ATACMS is a 300km range tactical ballistic missile.
Match made in heaven! M142 and C-130
Here is analogy 2, imagine an F-16 dropping a 1,000 lb bomb, done? Now the F-16 costs $60 million per jet and $22,000 per hour to fly minus crew training. Now M142 costs about a 20th of an F-16, but also travels at 10th the speed at half the combat radius. The 1000 lbs JDAM is equivalent to basically 6 different rockets that go a further 90km.
Hence, for the 20th of cost of platform you have a land based system that can strike targets (vehicle range + missile range) at three quarters of range and can easily operate in heavy AD environment. The key being that these operate behind your own lines and have well defined shoot and scoot tactics to avoid counter battery fire or being spotted and destroyed. The key here is that one M30/M31 rocket costs $110,000 so $660,000 for a 6 missile volley but each with a 100kg warheard whereas a 1,000 lbs JDAM costs $25,000. So you save some and spend some, cheaper platform firing a more expensive weapon versus a costlier platform firing a cheaper bomb with higher risk.
The idea behind this platform was to provide rocket artillery support ala Close Air Support to advancing or defending troops. The Ukrainians being the smart tacticians they are (not a sarcasm), use these as strategic weapons. They were hitting targets behind enemy lines that shaped the long term battle by hitting ammo dumps. This blunted the artillery advantage by a big margin thus bringing in parity. They hit key logistics and command nodes further altering the strategic scenario.
It has not been officially confirmed if they have the MGM-140 ATACMS as of early September 2022 but it remains a possibility if not active already. Even without the larger ballistic missile, every km of new frontline opens new angles and targets that can be hit. Given the strategic outlook in usage, the Ukrainians have just expanded the scope of the weapon and its use cases.
Other countries have their own comparable systems too. The Indians have Pinaka which has guided and unguided rockets slowly increasing the range to M30/M31 levels. The Chinese have a wider array of systems both in internal use and international use. Pretty sure these countries are observing the usage and planning their own tactics around the idea of everything is a strategic weapon if you want it to be.
Indian Pinaka in action!