After Congress approved a long-delayed $61bn in US military aid to Ukraine this week, Russia gloated that advanced western weapons would not turn the tide on the battlefield.

More than at any point since Vladimir Putin ordered the invasion of Ukraine two years ago, Russia’s president appears “very self-assured and happy” in recent months, said a person who knows him well. “Let’s see if the military aid changes that.”

While Ukraine was running out of western aid and struggled to rotate its exhausted troops, Russia took advantage of its superior firepower and manpower and made incremental advances across the front line.

Two senior Ukrainian intelligence officials described Russia’s current attacks along key areas of the frontline and missile and drones strikes on Kharkiv and similarly important cities as softening the battlefield before a bigger offensive operation.

The officials said they expected Russia to launch a new large-scale offensive in late May or June.

But with US aid finally on the way, Ukraine could expose the flaws inherent in Russia’s attempts to overwhelm it with low-quality munitions and a large but poorly trained army, according to western defence officials and analysts.

One western official said that while Russia might make some tactical breakthroughs at the frontline, it remained an ineffective army characterised by old equipment and poorly trained soldiers and would not “overrun” Ukraine, they added.

“In February 2022, Russia had a far better equipped and trained army,” the official said, referring to Russia’s initial invasion and subsequent rout in northern Ukraine. “I simply can’t see that it is better now.”

After its initial blitzkrieg failed, Russia has sought to grind down Ukraine by favouring quantity over quality on the battlefield.

Russia fires five shells for each returning salvo from Ukraine’s forces, while the ratio is even higher in some flashpoints along the line of contact, according to Dara Massicot, a senior fellow at the Carnegie Endowment for International Peace who studies the Russian military.

“The aid won’t cancel out Russian advantages this year, but it will allow Ukrainian forces to defend their positions with counter-battery fires and can be used to slow or halt Russian advances,” Massicot said.

Boosted by a record Rbs10.8tn ($118.5bn) in spending on defence this year — six per cent of gross domestic product — Russia’s arms industry has built up production several times over, with factories working around the clock, according to officials.

Sergei Chemezov, head of Rostec, the state defence conglomerate, last November said Russia was making 2.5 times more artillery and multiple launch systems than before, while increasing production of some types of ammunition by more than 60 times.

Those sheer numbers, however, mask Moscow’s inability to turn that firepower into a significant breakthrough — something Russian experts say it could only do with more advanced weaponry.

Western sanctions have made it harder for Russia to obtain the components needed for drones, loitering munitions, guided bombs, and high-precision missiles, forcing it to rely on the lower-tech weapons it can mass-produce more easily, according to Ruslan Pukhov, head of the Center for Analysis of Strategies and Technologies, a Moscow defence think-tank.

Pukhov said: “The most decisive systems on the battlefield in Ukraine are directly dependent on sanctions. Scaling them up means leaders on all levels have to think creatively and understand the main trends and likely outcomes of the war.”

Despite Moscow’s larger arsenal, its army “doesn’t have a radical advantage over Ukraine in artillery and munitions”, he added. “At least, the people fighting on the Russian side don’t see it.”

Instead, the Kremlin is deploying more low-tech weaponry such as highly destructive glide bombs and refurbished Soviet weaponry while deploying troops using motorcycles and off-road vehicles.

“If it works, it works — low-tech or not,” Massicot said.

Even that, however, is not enough to sustain the enormous rates of fire Russia rained down on Ukraine in the first six months of the war, according to Pavel Luzin, non-resident senior fellow at the Center for European Policy Analysis, based in Washington.

Russia fired up to 60,000 shells a day before autumn 2022 — an amount that has dropped to about 10,000 a day and which includes supplies from North Korea and Iran.

Those smaller rates of fire reflect how the intensity of battle is outstripping what Russia can replenish even at those higher production levels — and holding back a more significant push forward.

Russia would need to produce 3.6mn shells a year to sustain the current rate of fire, according to a report published this week by the Center for Strategic and International Studies.

The defence ministry has admitted, however, it can only produce at most half of the 4mn 152mm-calibre shells and 1.6mn 122mm-calibre shells Putin’s military estimates it needs to break through.

And as Russia keeps firing more shells, it wears down its artillery barrels faster than it can produce new ones — forcing it to replace them with Soviet-era barrels instead.

The US aid does not address what Ukrainian and western officials say is Kyiv’s most glaring problem — an inability to match the enormous numbers of men Russia has called up to fight.

Christopher Cavoli, Nato’s supreme allied commander for Europe, told lawmakers in a Senate armed services committee hearing in April that Russia is recruiting 30,000 soldiers per month, taking its frontline troops from 360,000 a year ago to 470,000.

To raise those men, the army is offering financial incentives including salaries starting at Rbs200,000 — five times the average wage in some of Russia’s poorer regions — and bonuses ranging between Rbs300,000 and Rbs1mn, according to a report by Estonia’s foreign intelligence service.

Soldiers can receive further bonuses for their exploits on the battlefield or being wounded, while their families stand to receive generous payouts if they are killed in action.

Those prospects are not distant: 315,000 Russian soldiers have been killed or wounded in the war, Cavoli said, adding pressure for the army to replenish its units.

That mercantile approach allows Russia to draw enough recruits from people for whom fighting is financially attractive while avoiding mobilisation — a step that prompted hundreds of thousands of men to flee the country in autumn 2022.

“The main approach now is ‘purchasing blood’ among the Russian lower classes,” said Luzin, from the Center for European Policy Analysis.

A summer offensive, however, would require Putin to declare another round of mobilisation, said Massicot of the Carnegie Endowment for International Peace.

“If the Kremlin has ambitions for Kharkiv, or something even more difficult like southern Ukraine, then they will need to generate a very large force, probably well over 100,000 for both, plus the equipment,” Massicot said.

Even if Russia did draft more men, sheer numbers would not be sufficient to compensate for their lack of training, Luzin said. “We all talk about mobilisation but where are the commanders, sergeants and lieutenants, who would command the mobilised soldiers?”