Ukraine’s military had only one Bohdana artillery cannon in its arsenal when Russia invaded the country two years ago. Yet that single weapon, built in Ukraine in 2018 and able to shoot NATO-caliber rounds, proved so effective in the earliest days of the war that it was trucked to battlefields across the country, from the northeastern city of Kharkiv to the southwestern coast along the Black Sea and points in between.

Now, Ukraine’s arms industry is building eight of the self-propelled Bohdana artillery systems each month, and although officials will not say how many they’ve made in total, the increased output signals a potential boom in the country’s domestic weapons production.

The ramp-up comes at a pivotal moment. Russia’s war machine is already quadrupling weapons production in round-the-clock operations. Ukraine’s forces are losing territory in some key areas, including the strategic eastern town of Avdiivka, where they withdrew from in February. A U.S. aid package is still hung up in Congress. And while European defense firms are gingerly opening operations in Ukraine, major American weapons producers have yet to commit to setting up shop in the middle of a war.

It is widely agreed that Ukraine needs to rebuild its domestic defense industry so that its military will not have to rely for years to come on the West, which has at times hesitated to send sophisticated weapons systems — including air defenses, tanks and long-range missiles. Whether that can be done in time to alter the trajectory of a war that would be all the more tenuous without more U.S. military aid remains to be seen.

But Ukraine’s military engineers have already shown surprising skill in jury-rigging older weapons systems with more modern firepower. And over the last year alone, Ukraine’s defense companies have built three times as many armored vehicles as they were making before the war and have quadrupled production of anti-tank missiles, according to Ukrainian government documents reviewed by The New York Times.

Funding for research and development is forecast to increase by eight times this year — to $1.3 billion from $162 million — according to an analysis of Ukraine’s military budget through 2030 by Janes, a defense intelligence firm. Military procurement jumped to a projected 20-year high of nearly $10 billion in 2023, compared with a prewar figure of about $1 billion a year.

“We say that death to the enemy starts with us,” Alexander Kamyshin, Ukraine’s Strategic Industries minister, said in an interview last month in his office in a nondescript brick building in Kyiv tucked away among restaurants and apartment blocks.

“It’s about showing that we don’t sit and wait until you come help us,” Mr. Kamyshin said. “It’s about trying to make things ourselves.”

Some weapons are proving harder to produce in Ukraine than others. They include 155-millimeter artillery shells, which are in dire need on the battlefield but depend on imported raw materials and licensing rights from Western manufacturers or governments. Mr. Kamyshin said domestic production of 155-millimeter shells was “on the way,” but would not say when.

Once a main supplier of the Soviet Union, Ukraine’s defense industry shrank over three decades of budget cuts after the country declared independence in 1991. The government in Kyiv now plans to spend about $6 billion this year on weapons made in Ukraine, including one million drones, but, Mr. Kamyshin said, “we can produce more than we’ve got funds available.”

The long period of decline may be hard to overcome. To restart production of the 2S22 Bohdana artillery cannon, for example, officials had to track down the weapon’s original designers and engineers, some of whom had been assigned to menial military tasks across Ukraine.

By June 2022, Ukrainian forces were using the Bohdana’s 30-mile range to target and destroy Russian air defenses in the successful battle for Snake Island in the Black Sea.

“It was a very big surprise for the Russians,” said Maj. Myroslav Hai, a special operations officer who helped liberate the island. “They couldn’t understand how somebody could use artillery for this distance.”

In Europe, political leaders who worry about eroding American support and business executives who see new market opportunities are promoting military production ventures in Ukraine, even if it may be several years before any of those weapons or materiel reach the battlefield.

The German arms giant Rheinmetall and the Turkish drone-maker Baykar are in the process of building manufacturing plants in Ukraine. France’s defense minister said in March that three French companies that produce drones and land warfare equipment were nearing similar agreements. Last month, Germany and France announced a joint venture through the defense conglomerate KNDS to build parts for tanks and howitzers in Ukraine and, eventually, whole weapons systems.

Experts said Ukraine’s military has positioned air defense systems around some of its most critical weapons factories. It’s likely that foreign-backed plants will largely be built in the country’s west, far from the front lines but also protected by air defenses.

Christian Seear, the Ukraine operations director for the Britain-based military contractor BAE Systems, said even the nascent moves by foreign producers send “a critical message — that you can go into Ukraine and set things up.”

While BAE Systems looks to manufacture weapons in Ukraine in the future, Mr. Seear said, the company is currently focused on a “fix it forward” approach, to repair battle-damaged weapons at factories in Ukraine to get them back to the front lines faster. Many of the weapons in Ukraine’s ground war — including M777 and Archer howitzers, Bradley and CV90 combat vehicles and Challenger 2 tanks — are manufactured by BAE Systems.

“We want to keep those things fighting, and it’s becoming quite clear that you can’t keep maintaining those assets in neighboring countries,” Mr. Seear said. “It’s not acceptable for a long-term war of attrition to have hundreds of high quality, reliable howitzers having to travel hundreds of miles.”

To date, Ukrainian and U.S. officials said, no major American weapons manufacturer has announced plans to open production lines in Ukraine. However, some senior executives have visited Kyiv in recent weeks to meet with Mr. Kamyshin and other officials, and the Biden administration hosted meetings in December to bring together Ukrainian leaders and U.S. military contractors.

Helping Ukraine rebuild its defense industry has become even more vital as Republicans in Congress have blocked $60 billion in military and financial aid to Ukraine. (However, Speaker Mike Johnson, Republican of Louisiana, recently signaled that he is looking for politically palatable ways to bring the aid package to a vote.)

But a web of bureaucracy in Kyiv threatens to slow at least some investors as they seek to push proposals through three ministries, Defense, Digital Transformation and Mr. Kamyshin’s Strategic Industries.

“We’re trying to get a sense of how this all fit together, and how they work together,” said William B. Taylor, a former ambassador to Kyiv who is leading an effort by the U.S. Institute of Peace to help link up American and Ukrainian defense firms.

“American firms have got a lot of opportunities to invest in other places around the world,” Mr. Taylor said. “This is one where U.S. national interests are at stake, so it’s why we would take an extra step to help make these connections.”

Since 155-millimeter caliber artillery rounds are desperately needed, Mr. Taylor suggested that an initial joint venture between Ukrainian and American firms could focus on ramping up their production.

European producers are already venturing into that market.

“If the Europeans will be involved in its development in the volumes they promise, I think we will solve the problem of ‘shell hunger’ over time,” Oleksandr Syrskyi, Ukraine’s armed forces commander, told Ukraine state media in an interview published on Friday.

Although Ukraine’s manufacturers are prohibited from exporting weapons until the war is over, Mr. Kamyshin sounds eager to compete with foreign arms producers.

A forceful speaker with a goatee and a topknot hair style traditionally worn by Ukrainian Cossacks, Mr. Kamyshin is one of what Mr. Taylor described as a new generation of leaders in Ukraine — at age 39, a young gun who has ascended rapidly through the government ranks.

After his appointment as minister, in March 2023, Mr. Kamyshin visited almost every weapons factory in Ukraine and said he found an industry badly in need of an overhaul. Workers were laboring in damaged factories in some places; in others, rockets were being built by hand.

Though he said production is moving more smoothly now, he still receives daily updates on critical assembly lines to rapidly identify breakdowns and get them fixed quickly.

“We are moving things faster and cheaper, and they work,” Mr. Kamyshin said in an interview that was as much a sales pitch for domestically built weapons as it was a discussion of foreign investments.

“We will join you and NATO one day,” he said confidently. “So if you procure from us, you’re building up abilities, and that will become part of the joint capabilities one day. So why not invest in your joint capabilities?”

Vladyslav Golovin and Oleksandra Mykolyshyn contributed reporting.