General Data
Weight: 136 lbs assembled; tube 44.5
lbs; mount 46.5 lbs; base plate 45 lbs.
Overall Length: 3 ft 9.5 in.
Muzzle velocity (HE): 700 f.p.s.
Rate of Fire: 18 rounds/min norm; 30-35 rpm
max
Rocket: M7A1 shaped charge,rocket motor ignited
electrically
Maximum Range (HE): 3290 yds
Sight: M4
Ammunition:
M43A1 Light HE: 6.87 lbs; range
min 200 yds; range max 3290; 80% frag radius 25
yds (comparing favorably with 75mm howitzer);
fast detonating fuse (explode on surface).
M45, M45B1 Heavy HE: 10.62 lbs;
range max 2558 yds; bursting radius comparable
with 105mm howitzer; equipped with delay fuse so
some penetration possible for demolition use.
M56 Heavy HE: 15.01 lbs; range
max 1300 yards; adjustable fuse for quick or
delay operation.
M57 WP (White Phosphorus): 10.74
lbs; range max 2470 yds; designed to lay down
screening smoke, but had definite anti-personnel
and incendiary applications.
M57 FS: 10.74 lbs, range max 2470
yds; laid down dense white smoke.
M301 Illuminating shell: range max 2200 yds;
attached to parachute; burned brightly (275,000
candlepower) for about 60 seconds, illuminating
an area of about 150 yards diameter; used M84
time fuse, adjustable from 5 to 25 seconds before
priming charge detonated, releasing the illum and
chute.
Each round has fins to stabilize
it in flight and cause it to strike fuze-end
first. The propelling charge consists of a
primer, an ignition cartridge, and (usu) four or
six removable propellent increments. The primer
and ignition cartridge are inserted in the base
of the fin shaft. The removable increments are
between the fin blades or the boom assembly. The
projectile is dropped down the barrel, fin end
first, the primer strikes the fixed firing pin
which detonates the primer and ignition
cartridge, which in turn ignites the propellent
increments, forcing the round out of the barrel,
carrying the primer and cartridge with it and
readying the mortar for the next round.
Discussion
Comparing weight of material to
destruction delivered at the target, mortars are
very efficient. 'The infantry's
artillery', they provided small infantry
units artillery-like fire support when artillery
either was not available, or could not be moved
forward fast enough. Normally, mortars are fired
in defilade, such as from the reverse side of
hills or ridges, which gives the gunners
protection from direct fire even though close to
the enemy. Therefore, the gun squads can be
emplaced, and ammunition resupply can be
centralized and stockpiled, permitting a heavy
volume of fire to be placed on any target within
range. This indirect fire relies on Forward
Observers, and aiming stakes, and is very
effective when done by experienced mortar
teams.
The initial Chinese Communist
assaults of November and December 1950, did not
bring artillery, but they did bring mortars, and
used them with great effectiveness. Typical CCF
assault tactics were to drift strong infantry
units near our lines at night, and use small
probing attacks to locate our automatic weapons
and machine guns and, if possible, junctions
between our platoons or other weak points. Then,
they would attack in strength with platoons armed
only with grenades, followed by submachine gun
platoons. Their light mortar units would follow
quickly, and place their fire on our strong
points from fairly close distances, enabling them
to fire with reasonable accuracy even though at
night and without accurate registration.
Our battalion's 81mm mortar
platoon, consisting of 6 mortars, were assigned
to the battalion's three rifle companies
depending on need, and were registered in before
nightfall so they could safely respond with
appropriate type ammo when called in. This
capability, particularly illum rounds, gave our
infantry quick support.
Moving the heavy base plate for
shifting to new and unregistered targets was
often a problem, particularly in the vicious
sub-zero cold of North Korea. Getting a stable
base plate, for un-registered fire at night,
without endangering forward units who needed very
close support, was a manual art. With the FO on
the communication line, and some strong guy
digging new base positions in the frozen earth,
it could be done, however, and it was done time
and again.
Our 60mm
guns, usually in three gun sections in a mortar
platoon reinforcing each Rifle Company, were
invaluable in closer support. Sometimes in
battery, but usually assigned one gun per
platoon, they moved fluidly close behind our
assault troops, and registered on assault lanes
in front of the platoons before night, so as to
be ready to quickly counter enemy night
assault.
They often had to.
