The US on Wednesday promised $800 million more in weapons for Ukraine as the Russian invasion enters its third month and Russian forces threaten to take the southern city of Mariupol and hammer the capitol Kyiv with missile strikes.

Ukraine’s military has made impressive use of the weapons that NATO members provided prior to the invasion and over the past several weeks, including portable missile launchers and artillery. Despite Russia’s superior armament, Ukraine’s forces have been able to take advantage of Russian forces’ poor planning and tactical blunders in many cases to retain control of most major population areas. However, the Ukrainian government has been calling for additional weapons, particularly fighter jets, to continue to hold off Russian forces, which NATO as a whole has thus far refused to give. Poland had offered fighter jets to the Ukrainian government last month but the plan was scrubbed after the US stepped in to stop it.

The new US pledge is set to include some aircraft, Reuters reported Thursday, although not the fighter jets Ukraine has been asking for to fend off Russian airpower; instead, 11 Russian-made Mi-17 helicopters, originally meant for US forces in Afghanistan before last summer’s chaotic departure, have been committed to Ukraine. While they’re not as agile as fighter jets, such as MiG-29s or F-16s, some variants of the Mi-17 can be fitted with anti-tank missiles and other weapons to attack Russian ground and air forces. The US already provided five Mi-17 helicopters to Ukraine earlier this year.

Powerful weapons systems like howitzers — essentially portable field cannons that can shoot projectiles at long trajectories, including precision guided munitions — are also headed to Ukraine, along with armored personnel carriers and other vehicles, hundreds of portable Switchblade drone munitions, millions of rounds of ammunition, and a variety of other defense systems and protective gear, have also been earmarked for Ukraine. The Pentagon on Sunday confirmed to Vox that weapons shipments were already underway, although a spokesperson did not give specifics and did not answer questions about the helicopters in particular, including the specific model the US would be sending to Ukraine.

New weapons offer new advantages and challenges

“They are receiving a great amount of what they need,” Rita Konaev, associate director of analysis at Georgetown University’s Center for Security and Emerging Technology told Vox on Sunday, despite Ukraine’s continued pleas for fighter jets to counter the Russian air force. “It’s unprecedented. We have not seen this much [weaponry] of this caliber, this fast.”

The howitzers, in particular, as well as the armored vehicles, have been on a wish list of the weapons the Ukrainian armed forces desperately need to stave off Russian forces as fighting concentrates in the southeast, in the Donbas area. That equipment represents a significant capability increase as Ukraine tries to stave off Russian forces, John Spencer, an urban warfare expert at the Madison Policy Forum, told Reuters. “You need these bigger, more powerful weapons … to match what Russia is bringing to try to take eastern Ukraine,” he said.

Russia is expected to ramp up fighting in Donbas in the east in the coming days and weeks, making the swift delivery of the new weapons and equipment crucial. A Russian victory looks imminent in Mariupol, which Russian forces have bombarded and cut off access to basic necessities and humanitarian aid for weeks, and they could use the same brutal tactics to claim other Ukrainian towns and cities. With that shift in mind, spokesperson John Kirby told reporters on Wednesday that the Pentagon was sending out the new weapons package as quickly as possible.

“You’ve seen us go in the past from the time the president authorizes drawdown until the first shipments actually start landing in the region can be as little as four to five days,” Kirby said. “And then another couple of days… once they’re there to get processed and actually in the hands of Ukrainian frontline forces,” Kirby told reporters, noting that although there would be some procedural red tape to go through regarding the new package, “we’re not going to wait, we’re going to start getting these articles on the way as well. So, we will literally start right away.”

Because some of the weapons systems — namely, the howitzers and Switchblades — are new to Ukrainian troops, there will be a learning curve in the midst of a very active conflict. However, Kirby told reporters on Thursday that he doesn’t think training Ukrainian troops on the new weapons will be much of a lift; in fact some Ukrainian troops have already been trained to use the Switchblades, according to the New York Times.

“While some of these systems, the radar, the howitzers, will require some familiarization and some basic training … it’s not exorbitant,” he said. “It won’t take a long time. It won’t require a large pool of trainees. We’ll work it out. We’ll try to get opportunities for a small number of Ukrainians to be familiarized with these systems. But we don’t believe that it’s going to be an onerous task or lengthy in time or in resources.”

But the Biden administration’s new commitment, both in weapons and in a timely delivery and training, has prompted a rebuke from Russia, as the Washington Post’s Karen DeYoung reported on Thursday.

“We call on the United States and its allies to stop the irresponsible militarization of Ukraine, which implies unpredictable consequences for regional and international security,” a formal diplomatic note delivered from the Russian embassy to the US State Department warned.

The Post reported that the note could mean Russia intends to begin attacking weapons supplies coming into Ukraine; thus far, Russian forces have not done so, although they consider weapons convoys legitimate military targets. It’s also not outside the realm of possibility that they could attack weapons depots outside Ukraine’s borders, according to George Beebe, the former CIA director of Russia analysis. “There has been an assumption on the part of a lot of us in the West that we could supply the Ukrainians really without limits and not bear significant risk of retaliation from Russia,” he told the Post. “I think the Russians want to send a message here that that’s not true.”

Can the new weapons make a difference?

A more positive spin on the note comes from a senior US official, who told the Post that Russia’s warning is an indication that US and NATO’s weapons shipments to Ukraine are working as intended.

“What the Russians are telling us privately is precisely what we’ve been telling the world publicly — that the massive amount of assistance that we’ve been providing our Ukrainian partners is proving extraordinarily effective,” the official said. While US and NATO weapons have certainly played a significant part in the Ukrainian defense — and these new weapons are likely to prove effective in this new phase of the conflict — there are complicating factors to take into consideration when assessing the effectiveness of the new cache of weapons making its way to Ukraine.

First of all, while the howitzers and radar equipment in particular will help Ukraine’s armed forces achieve something approaching parity with Russian forces in terms of armament, that’s fairly specific to this theater, Konaev said. Since the fighting has moved out of urban centers and into more “open range, open space” contexts, she said, “hardware could matter in a more significant way.” Ukrainian forces are losing the defensive edge they had in urban contexts, and so being able to detect and attack Russian weapons systems more effectively could provide an advantage.

But again, that advantage is contextual, and even though Ukrainian troops will receive some sort of training on how to use the new weapons, it’s unclear what kind of maintenance support they’ll get. “We’re talking about quantity and type,” Konaev said. “We’re not talking sufficiently talking about survivability of equipment.” Things like repairs, spare parts, and critical software upgrades are crucial to making sure equipment is durable and can be used sustainably in a war that has no end date.

Less exciting than drone munitions, mines, and ammunition — but perhaps just as critical — is the protective equipment the US is sending over. Despite heavy losses, Russia can theoretically keep replenishing its troops in Ukraine, should it decide to do so. “We don’t know what Ukraine’s bench looks like; they don’t have the ability to replenish forces,” Konaev told Vox. Keeping Ukrainian troops alive and able to fight will be a critical part of continued assistance.

But larger questions — of what the desired and realistic outcomes of this conflict are, and what a long-term strategic partnership to support Ukraine in this war should look like — are yet unanswered. Other than a triumph of democracy over authoritarianism, specific, measurable strategic goals of US support haven’t been clearly articulated. In other words, Konaev said, we don’t know if the goal is for Ukraine, “to win? When? How? And at what cost?”

Sending weapons is critical for Ukraine to defend itself against an unjust and devastating Russian invasion; that’s indisputable. But it only serves an immediate need, and it’s narrow in scope; defensive support doesn’t address the great humanitarian devastation Russia is causing in population centers as part of its military strategy. The US and allies have promised humanitarian and economic aid, which must be part of its long-term support for Ukraine. In the immediate term and in the long term, weapons are not the only critical need; food, shelter, medication, and medical care are arguably just as important for the Ukrainian population, and will continue to be for long after the fighting stops.