Russian forces have been pounding Ukrainian troops in the Donbas region with combined short-range ballistic missiles, heavy artillery, tanks, and multiple-launch rocket systems (MLRS). With Moscow making gains, “senior Ukrainian officials, including President Volodymyr Zelensky, have pleaded in recent weeks for the U.S. and its allies to provide the Multiple Launch Rocket System, or MLRS,” and another weapon called the High Mobility Artillery Rocket System, or HIMARS, CNN reports.

The Biden administration is leaning toward including them in the next military aid package. What are these advanced weapons, and should the U.S. ship to Ukraine?

What is happening in Ukraine?

Russia has made “made steady, incremental gains in heavy fighting in eastern Ukraine in the past several days, though Ukrainian defenses remain effective overall,” the Institute for the Study of War think tank assessed last Thursday. Several Ukrainian officials describe the situation as “very difficult.”

Indeed, the situation on the eastern front lines “is as dire as people say,” Ukrainian Foreign Minister Dmytro Kuleba said in a video Thursday night. “We need heavy weapons. The only position where Russia is better than us, it’s the amount of heavy weapons they have. Without artillery, without multiple launch rocket systems, we won’t be able to push them back. If you really care for Ukraine, if you want Ukraine to de-occupy its territories, send us multiple launch rocket systems as soon as possible.”

What are the MLRS and HIMARS, and why does Ukraine want them so badly?

The U.S. version of the MLRS can fire a barrage of rockets up to about 185 miles, depending on the type of munition used. That’s much further than the 18-mile range for the M777 howitzers the U.S. has already provided — or anything else Ukraine has. The HIMARS is a lighter, more mobile cousin of the MLRS that uses some of the same missiles. Ukraine’s Ministry of Defense posted a video of a Russian multiple rocket launcher to demonstrate why it needs U.S.-made MLRS weapons. 

“The Ukrainians have asked for MLRS systems” because they “provide greater range and greater firepower than a typical artillery system,” a senior Pentagon official said Thursday. “The Ukrainians have made it clear — and we don’t disagree — that this fight in the Donbas is a fight that’s heavily reliant on long-range fires.” The official added that “no final decisions have been made” about the next military aid package “either in terms of what it’s going to include and when it’s going to be announced.”

Why wouldn’t the U.S. give Ukraine these weapons?

The Biden administration is a little concerned about “whether the U.S. could afford to give away so many high-end weapons drawn from the military’s stockpiles,” but a “major hang-up” has been “the rocket systems’ extensive range,” CNN reports. The White House has been wavering “amid concerns raised within the National Security Council that Ukraine could use the systems to carry out offensive attacks inside Russia,” and whether Russia would view such military aid as “a provocation that could trigger some kind of retaliation against the U.S.”

Russian Foreign Minister Sergei Lavrov suggested the answer to that last question could be yes. To defeat Russia on the battlefield, the West needs “to pump weapons to Ukrainian nationalists, the Ukrainian regime, including weapons that can reach the Russian Federation,” Lavrov told RT Arabic. “These are the weapons that Zelensky publicly demands,” but “we warned the West in the most serious way that they are already, in fact, waging a proxy war with the Russian Federation” and “this will be a serious step towards an unacceptable escalation.”

Why might the U.S. give Ukraine MLRS and HIMARS anyways?

The U.S. is heavily invested in Ukraine winning this war and Russia losing. “What I can tell you for sure,” the senior Pentagon official said, is that the Defense Department “is committed to helping Ukraine for as long as we possibly can.”

“We are in great need of weapons that will make it possible to engage the enemy over a long distance,” Ukraine’s top military commander, Gen. Valeriy Zaluzhnyi, said Thursday. “And this cannot be delayed, because the price of delay is measured by the lives of people who have protected the world from [Russian fascism].”

“I think it could be a game-changer, to be honest with you,” Rep. Jason Crow (D-Colo.) told CNN. Russia’s conventional artillery has a range of a little over 30 miles, so it “would not get close” to Ukrainian population centers if MLRS systems were stationed there, he added. “It would take away their siege tactics.”

“Giving the Ukrainian Army the ability to defend against Russian weapons like this, using HIMARS & MLRS systems, is a strategic no-brainer,” argued Mick Ryan, a recently retired Australian general who has been following the war very closely. “They are needed rapidly, and they are needed in quantity.” Rob Lee, a Russia defense policy expert at the Foreign Policy Research Institute, agreed. “This is a big deal and it is a significant factor in whether Ukraine will be able to retake terrain from Russia over the summer.”