The Biggest Mortars In Ukraine Are Slow, Devastating Siege Weapons

The Ukrainian army’s giant mortar is something of a mystery. We don’t know where the Ukrainians got their 240-millimeter M240 or M240s. Nor do we know which ammunition types they’ve got.

We do know the identity of one Ukrainian unit using the M240—and where. The Ukrainian navy’s 35th Marine Brigade has deployed at least one of the huge mortars near Marinka in eastern Ukraine’s Donbas region.

The M240 is the closest thing in modern armies to a siege weapon. Cumbersome and somewhat lacking in range but extremely powerful, the M240 can level city blocks or smash deep entrenchments from up to 12 miles away.

Prior to an M240 first appearing in Ukrainian service in September 2022, the only example of the huge mortar that anyone outside of the army ever had seen in Ukraine belonged to a museum in Kyiv.

It’s possible the Ukrainians activated this museum piece. It’s also possible there were 50-year-old, ex-Soviet M240s moldering in some obscure warehouse somewhere in Ukraine. Less likely, one of Ukraine’s allies—Romania? The Czech Republic?—may have donated one or more of their own ancient M240s.

Soviet firm Uraltransmash manufactured hundreds of towed and self-propelled M240s between the late 1960s and late ’80s. The Russian army rolled into Ukraine last February with at least a few of the self-propelled 2S4s—and promptly lost four of them to Ukrainian counterbattery fire.

The weapon’s sluggishness makes it especially vulnerable to enemy artillery. While a self-propelled 2S4 might be somewhat nimbler than a towed M240, both versions require either a large crew—up to 11 people—or a crane for reloading their 300-pound shells. An M240 can shoot just one round a minute.

The giant mortar doesn’t exactly require precision, but there is a laser-guided version of its high-explosive bomb—the 3F5. The Soviet army first deployed the 3F5 in Afghanistan in April 1985, to devastating effect.

The crew first lobbed two unguided rounds at their target—a mujahideen fortress—to calibrate the mortar. Next, they fired a 3F5 round “which penetrated the roof of the fortress,” analyst Lester Grau wrote in a 2006 study. “The fortress disappeared in a cloud of smoke, dust and debris. The mission took 15 minutes.”

We’ve seen Russian forces fire a few 3F5s in Ukraine, but there’s no evidence—yet—that the Ukrainians have used the same guided rounds. And for good reason. As Ukraine’s M240 might literally be a museum piece, its operators may not have access to 3F5s.

Ukrainian forces reportedly captured a stock of 240-millimeter mortar bombs during the Russian retreat from Kharkiv Oblast last fall. This stock could have included a few 3F5s.

But actually using the guided rounds also requires a fair amount of supporting equipment: a 1D15 laser-designator and 1A35I relay at the forward observation post, plus a 1A35K relay at the firing position.

After calibrating with unguided rounds, the crew fires a 3F5. The 1A35K relay then connects to the 1A35I relay and triggers the laser designator, which illuminates the target for the incoming shell.

Unless the Ukrainians had a stash of relays and designators in a museum or warehouse, or some ally donated the systems, the marines strictly are shooting unguided rounds from their giant mortar or mortars.

Which is fine. A 300-pound mortar bomb doesn’t need to land anywhere near its target to inflict a lot of damage. Precision isn’t an M240 crew’s biggest concern. Speed—their lack thereof—is what they should worry about.