A howitzer is a long-range artillery piece that fires an explosive shell on a high trajectory, in contrast to a cannon which fires directly. The shipment is part of two $800 million aid packages announced by the US.
Washington is sending the M777 variant, while Canada is supplying a much smaller number but has also included advanced, guided artillery shells.
Unlike howitzers supplied by European nations, which are built into armoured vehicles known as self-propelled guns, the M777 is towed into battle or carried by helicopter.
An artillery workhorse
Western countries have been sending cutting-edge weaponry to the Ukrainians — from laser-guided anti-aircraft missiles to anti-tank missiles that can anticipate the final location of a moving target — following the Russian invasion on February 24.
By contrast, the US first used a 155mm howitzer — the M114 — in 1942, while France fielded a variant of the big gun even earlier. The US military also uses a lighter 105mm version.
During their long history, the design of howitzers has constantly evolved, keeping them an integral part of military operations.
“Field artillery has experienced tremendous change since the end of World War Two, and the pace of that change has accelerated in recent years as technology in ISR [intelligence, surveillance, and reconnaissance] integration and C2 [command and control] has enabled more effective, efficient, and precision ‘fires’,” John Grenier, a historian at the US Fires Centre for Excellence, a US military training centre, told The National.
Upgrades to 155mm howitzers, from the use of strong and lightweight materials such as titanium to advanced “fire control” systems that use GPS, make it a very different system to its predecessors, which bombarded enemy forces in the Second World War and the Korean and Vietnam wars.
“The US Army's number one modernisation priority as it prepares for large-scale combat operations is long-range precision fires,” Mr Grenier said, referring to accurate artillery.
The Second World War variant of the 155mm howitzer typically had a range of between 15 and 22 kilometres depending on the type of ammunition, which included shells filled with steel balls for use against soldiers in the open and high-explosive rounds for smashing into bunkers.
Today, the M777 can hit targets up to 50km away with the Excalibur M982 round, which glides through the air with the aid of fins and is guided by GPS. The shell is reportedly accurate to within four metres. Another type of guided shell, although not as accurate as the Excalibur, is the M549.
The higher accuracy of modern shells has transformed the use of artillery, which previously required heavy logistical support.
Armies would have to stockpile hundreds of thousands of shells to rain down on enemy positions, with many failing to land within 200 metres of the target.
Today, just six Excalibur rounds are enough to destroy an enemy command post, according to US testing, whereas 54 M549 shells would be required for the same job. For standard unguided shells, that number rises to nearly 80.
“A trade-off within field artillery traditionally has been among rate of fire, ‘throw weight’ [the weight of the payload] and accuracy.
“Today's computerised and constantly evolving fire-control systems allow soldiers to place fires on target at rates and with accuracy that were unimaginable during even Desert Storm in 1991,” Mr Grenier said, referring to the operation to liberate Kuwait from Iraqi forces.
“If soldiers can accomplish with one artillery round what used to take more than one shot, throw weight can become moot.”
The lightweight howitzer
The M777 is also far lighter than previous versions of the 155mm howitzer, weighing 3.745 tonnes compared to 7.25t for the M198 that saw service in the Vietnam War and First Gulf War.
If the extremely accurate Excalibur shells are not available to all howitzers supplied to Ukraine, the M777 can fire M795 shells that have a “circular error probable” of 100 to 260 metres — meaning half of all shells fired will land within that radius of the target.
Modern artillery use has changed in other ways too, primarily the ability to spot the enemy.
In the Second World War and later conflicts, soldiers known as forward observers would locate the enemy and spot where the artillery fire was landing, and radio back adjustments if it was off target.
Today, both Russian and Ukrainian forces are using drones, completely transforming the battlefield.
“The drone operator is replacing, in large part, the role of a forward observer. Moreover the drone operator (when he is aware of his own position, which is mostly not a problem) has a better overview over the target zone then a forward observer on the ground would ever have,” Tim de Zitter, an analyst with the Belgian Ministry of Defence, told The National.
The US has also supplied Ukraine with Firefinder radar systems, designed to quickly locate the exact position of enemy artillery.
How powerful are howitzers?
Chris Cobb-Smith, a former British Army artillery officer, says that European self-propelled 155mm howitzers currently en route to Ukraine might prove more powerful than the towed variety from the US.
Self-propelled guns typically have longer barrels, giving them greater range and a higher rate of fire than towed guns. Either way, supplying Ukraine with 155mm guns will significantly boost the firepower of its forces.
“The effect of a 155 is significantly more impressive than a 105mm – despite the seemingly minimal difference in calibre. The wide open spaces of the East is ideal for the self-propelled 155mm,” Mr Cobb-Smith told The National.
This extra power compared to US M777s may not be a huge overall advantage, he added, noting that “towed artillery can be moved around far quicker” over long distances due to its lighter weight compared to self-propelled guns.