Russo-Ukrainian War: The M240 240mm Heavy Mortar

Source: Reddit

     A soldier of the 3rd. Assault Brigade poses next to one of the unit's handful of colossal M240 240mm heavy mortars. The M240 mortars in use by Ukraine had been in storage until an unknown number were withdrawn, refurbished, and put back into service. Today, the M240 is the largest mortar in operational service in the world. Sometimes classified as a siege mortar, the M240 is designed to bombard fortified positions and the initial design commenced in 1944, being a scaled up version of the PM-43 160mm heavy mortar. Prototypes of the M240 were tested into 1950 and once accepted for service, production started in 1951 with units receiving the M240 commencing in 1953. In total, 329 examples of the M240 were built when production ended in 1958.

     With a combat weight of 4.6 tons and a barrel length alone of 17.6 feet, the M240 requires a maximum crew of 11 to operate effectively. A tow vehicle (usually a MT-LB tracked prime mover or a Ural 373 series 6x6 truck) moves the M240 about as well as carries the crew. Between one to two additional vehicles normally accompany the mortar with one containing ammunition while the other carries equipment and apparatus to assist in emplacing the M240 into a chosen firing position. The maximum tow speed is 25 miles per hour.

     The barrel is of the smooth-bore type and uses a breech-block. The 2-wheel carriage permits a total traverse of 18 degrees and the barrel can be elevated to a minimum of 45 degrees to a maximum of 65 degrees. Both traverse and elevation is manually controlled using gears situated on the left side of the barrel. Sighting is done using older MP-46 or MP-46M panoramic sights or by using a K-1 collimator sight. The carriage is equipped with a recoil assembly, used to reduce firing vibration and be the bridge between the barrel and the mount.

     Loading the M240 is no simple process. As the mortar is a breech loader and cannot be loaded while the barrel is elevated, the barrel is brought down to a horizontal position. The standard 3OF-864 HE (High-Explosive) bomb has a total weight of 290 pounds of which 75 pounds accounts for the explosive in the bomb's warhead. The bomb is brought to the M240 using a 2-wheeled trolley and once near the breech, long-handled tongs are used to pick up the bomb with two men on either side of the projectile providing the lift. A fifth man stands behind the bomb, making sure the bomb's fins are steady and not damaged. Once the bomb is pushed into the barrel, the breech is closed and the M240's barrel returned to battery. A well trained crew can manage a rate of fire of 1 round per minute.

     The M240 is capable of lobbing the 3OF-864 bomb out to a maximum range of 6 miles. A RAP (Rocket Assisted Projectile) version of the 3OF-864 (designated the 3F2 Gagara), fitted with 3M15 rocket motors, can extend that range out to 12 miles. However, even with the RAP bomb, the M240 is within counterbattery range of guns such as the 122mm D-30 howitzer, BM-21 Grad MLRS (Multiple Launch Rocket System), and drones such as the ZALA Lancet loitering munition as well as other FPV drones. Bringing the M240 into action takes up to 25 minutes from the halt and with apparatus to assist with the set up. The M240 can only fire from firm ground and if the ground is too hard, explosive charges are used to blow a pit into the ground for the base plate to settle into. While preparing to fire may go unnoticed, after the first bomb is fired, detection may only be a matter of time. It takes up to 15 minutes to return the M240 to traveling condition and this makes “shoot and scoot” tactics of very limited value. This issue is the main reason the Soviet Union developed the 2S4 Tyulpan (“Tulip”) which is a tracked, self-propelled mounting of the 240mm 2B8 mortar (a modified M240) that entered service starting in 1975.

     Other than the common 3OF-864 ammunition, it is believed the Ukrainians also have some stockpiles of the 3F2 Gagara bombs and a more limited availability of the 1K113 Smelchak (“Daredevil”) semi-active, laser-guided mortar bomb. The latter is composed of a 3F5 240mm HE projectile, a optoelectronic correction head, four adjustable fins, and six solid-fuel rocket motors. In order to effectively utilize the 3F5 bomb, it requires soldiers on the ground equipped with either a 1D15 or 1D20 laser rangefinder/designator. The 1D15 has a maximum range of 3 miles while the 1D20 has a 4 mile maximum range. The 1K113 itself has a maximum range of 5.7 miles.

     Doctrine in using the 1K113 as designed involves aiming the M240 towards the designated target and firing a standard round. The observation team, already in place (and usually no more than 5 miles from the target), reports the impact and calls back adjustments to the firing unit. After the gunner makes the corrections, the 1K113 is then loaded and fired. The soldier manning the 1D15 or 1D20 unit aims the designator at the target where it receives a radio signal from the M240 firing position regarding the bomb's trajectory. As the bomb nears the target, the designator switches to targeting mode, “painting” the target with laser pulses which the bomb's correction head picks up via reflection. Around .5 of a mile from impact, the rocket motors are utilized to make any corrections to the flight path to ensure successful impact. The usual deviation from the aim point is no more than 1.8 meters.

     As of July 28, 2025, the Russians have lost a total of sixty-one 2S4 Tyulpan (10% of the total production run) while the Ukrainians have not lost any of their M240 towed mortars.