Each unit armed with a mortar weapon system gives examinations semiannually. Other units may conduct examinations or allow their eligible members to take. 90(FM ). MORTARS. DECEMBER DISTRIBUTION RESTRICTION: Distribution authorized to U.S. Government agencies and their contractors only. Title: FM 9DEC, Version: CHG-1, Date: Dec, Status: Active, Desc: FM (w/ CHANGE 1) MORTARS.

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If the mortar section is to operate quickly and effectively in accomplishing its mission, mortar squad members must mortaars proficient in individually assigned duties. Correctly applying and performing these duties enables the mortar section to perform as an effective fighting team. The section leader commands the section and supervises the training of the elements. He uses the chain of command to assist him in effecting his command and supervising duties.

The mortar squad consists of three soldiers. Each squad member is cross-trained to perform all duties involved in firing the mortar.

The positions and principal duties are as follows:. The squad leader is in position to best control the mortar squad. Morrars is positioned to the right of the mortar, facing the barrel.

He is also the FDC. The gunner is on the left side of the mortar where he can manipulate the sight, elevating gear handle, and traversing assembly wheel. He places firing data on the sight and lays the mortar for deflection and elevation. Assisted by the squad leader or ammunition bearerhe makes large deflection shifts by shifting the bipod 23-900.

The ammunition bearer is to the right rear of the mortar. He prepares the ammunition and assists the gunner in shifting and loading the mortar. He swabs the barrel every 10 rounds or after each end of mission. The mm mortar, M, can be fired in the conventional mode or handheld mode Figure 23-0 mortar is a muzzle-loaded, smooth-bore, high-angle-of-fire weapon.

It can be drop-fired or trigger-fired and has five major components. The cannon assembly Figure has one end closed by a base cap. The base cap end of the cannon has cooling fins on the outside, which reduce heat generated during firing. Attached to the base cap end is a mortqrs carrying handle and firing mechanism.

The carrying handle has a trigger, firing selector, range indicator, mortrs auxiliary carrying handle. On the outside of the barrel is an upper and a lower firing saddle. The lower saddle is used when firing at elevations of to mils; the upper saddle is used when firing at elevations of to mils. The baseplate, M7, Morttars is a one-piece, circular, aluminum-forging base. It has a ball socket with a rotating locking cap and a stationary retaining ring held in place by four screws and lock washers.

The locking cap rotates mils, giving the mortar full-circle firing capability. The underside of the baseplate has four spades to stabilize the mortar during firing. The baseplate, M8, Figure is a one-piece, rectangular, aluminum-forging base. It should be used when the mortar is fired morrars the handheld mode. The baseplate allows the mortar to be fired mils left and mils right of the center of sector for a total sector coverage f, mils.

It has a socket in which the barrel can be locked to the baseplate by securing the locking arm. The underside of the baseplate has four spades to strengthen and stabilize the mortar during firing. Two spring-loaded plungers lock the baseplate to the barrel in its carry position. The bipod assembly Figure can be assembled to the 2-90 either before or after assembly of the barrel to the baseplate. It consists of seven subassemblies. The collar assembly, with an upper and lower half, is hinged on the left and secured by a locking cm on the right.


The collar fastens in one of the two firing saddles depending on the elevation being firedsecuring the bipod to the barrel. Two shock absorbers located on the underside of the collar assembly protect the bipod and sight from the shock of recoil during firing.

The traversing mechanism moves the collar assembly left or right when the traversing hand crank is pulled out and turned. The hand crank is turned clockwise to move the barrel to the right, and counterclockwise to move the barrel to the left. The left side of the traversing mechanism has a dovetail slot to attach the sight to the bipod.

The elevating mechanism is used to elevate or depress the barrel by turning the hand crank at the base of the elevation guide tube. This assembly consists of an elevating spindle, screw, hand crank, and housing elevation guide tube. The housing has a latch to secure the collar and shock absorbers to the housing for carrying. The hand crank is turned clockwise to depress, and counterclockwise to elevate.

The right leg assembly has no moving parts. It consists of a foot, tubular steel leg, and hinge attached to the elevating mechanism housing. The left leg assembly consists of a foot, tubular steel leg, hinge attached to the elevating mechanism housing, locking nut, and fine cross-leveling sleeve. It is used to lock the elevation housing in place. The spread cable is a plastic-coated steel cable attached to the bipod legs, which controls the spread of the two tubular steel legs.

A snap hook is fixed to mottars cable to secure the bipod legs when they are collapsed for carrying. Safe operation of the mm mortar requires that training include drill practice on tasks for safe manipulation and effective employment.

Crew training achieves the speed, precision, and teamwork needed to deliver responsive and effective fire on target. Before the mortar is mounted, the squad must perform premount checks. Each squad member should be capable of performing all the premount checks.

FM Chptr 9 Gunner’s Examination

When all pieces of equipment are checked, the gunner notifies the section leader by announcing, “All correct. The squad leader picks up and places the sight case and two aiming posts at the exact position where the mortar is to 23-900 mounted. The ammunition bearer places the outer edge of the baseplate against the baseplate stake. He aligns the left edge of the cutout portion of the baseplate with the right edge of the baseplate stake.

He then rotates the socket cap so that the open end points in the direction of fire. The gunner picks up the bipod with his left hand on the traversing hand crank and his right hand on the dovetail slot. He moves forward of the baseplate about 12 to 15 inches and faces the baseplate on line with the left edge gunner’s viewpoint of the baseplate.

Dropping down on one knee in front of the bipod, the gunner supports the bipod with his left hand on the gear case. He then detaches the hook and unwraps the cable assembly.

The gunner places his left hand on the midsection of the traversing slide and his right hand on the mechanical leg, and he extends the bipod legs the length of the cable assembly. He then aligns the center of the bipod assembly with the center of the baseplate.


He ensures that the elevation guide barrel is vertical and the locking nut is hand tight. The gunner moves to the mechanical leg side and supports the bipod with his left hand on the shock absorber. He unscrews the collar locking knob to open the collar.

The ammunition bearer picks up the barrel and inserts the spherical projection of the base plug into the socket. He rotates the barrel 90 degrees to lock it to the baseplate. If performed properly, the carrying handle is on the upper side of the barrel, facing skyward. The gunner pushes down on the shock absorber and raises the collar assembly.

The ammunition bearer lowers the barrel and places the lower saddle on the lower part of the collar. The gunner closes the upper part of the collar over the barrel. He replaces the locking knob to its original position and makes it hand tight.

The ammunition bearer cranks the elevation hand crank up 15 to 17 turns. The gunner takes the sight out of the case and sets a deflection of mils and an elevation of mils. He mounts the sight to the mortar by pushing the lock latch on the sight inward.

FM 23-90 (w/ CHANGE 1), ARMY FIELD MANUAL: MORTARS (09-DEC-2002)(TO 11W2-5-13-21)

He slides the dovetail on the sight into the dovetail slot on the bipod until firmly seated. The gunner releases the latch. He should tap up on the bottom of the sight to ensure proper seating.

He then levels the mortar first for elevation mils, and then cross-levels. The gunner announces, ” gun number up,” to 239-0 squad leader. Roofs or overhanging tree branches can cause overhead interference.

The gunner must be sure the round does not strike any obstruction. After the mortar is mounted, the gunner checks it thoroughly. He determines mask and overhead clearance by sighting along the top of the barrel with his eye placed near the base plug. If the line of sight clears the mask, it is safe to fire. If not, he may still fire at the desired range by selecting a charge zone having a higher elevation for that particular range.

When firing under the control of an FDC, the gunner reports to the FDC that mask clearance cannot be obtained at a certain elevation. Therefore, if the mask is not regular throughout the sector of fire, the minimum mask clearance is determined to eliminate the need for checking on each mission. To do this, the gunner depresses the barrel until the top of the mask is sighted. He then levels the elevation bubble and reads the setting on the elevation scale and elevation micrometer.

That setting is the minimum mask clearance. The gunner notifies dm squad leader of the minimum mask clearance elevation. Any target that requires that elevation or lower cannot be engaged from that position.