Q. What were the specs on the M-110 and the M-107?
A. There were different models and
there are several websites that have specs on the M-107 and M-110 but
generally, it weighed approximately 31.2 tons and had a top speed of 34mph.
It had a cruising range of 325 miles and was powered by diesel fuel (1.3
mpg) with a capacity of 300 gallons. Its length was 35.3 ft. and its height
was 10.3ft. Some Battery mechanics removed governors and made other
modifications strictly not in the books to boost speed.
Q. How many men were in a gun section?
A. Although the specs called for 13
• Gunner on gun mount left
• Gunner on gun mount right
• Two loaders on gun mount right
• Driver in hull left front
• 8 in support vehicle
there usually would be as many 7 men (a Section Chief, Gunner, Ass't Gunner,
Driver, three or four ammo humpers) or as few as 4 (a gunner, asst gunner,
powder and projo humpers).
Q. How many were inside the gun when it
A. There is only room inside for
Q. How long did it take to set up after a
A. Set up could be 20 minutes for a
hip shoot (A hip shoot is when they stop at the first clear area to set up
their guns; fire off one round to check aim and make corrections; then the
entire battery fires off rounds. The battery then quickly packs up and
continues on to their scheduled position) after finding battery center and
using an aiming post. For a more permanent firebase set up, it could be a
few hours preparing a parapet with a berm to dig in the hydraulic spade.
Some parapets had wood timbers for the tracks to rest on while using the
berm to back up into. The Seabees built parapets at Gia Le for the 83rd upon
moving north to Camp Eagle from down south.
Q. What was the range of the 8-inch
A. The range varied from 16,800 meters
(10.5 miles) to 30,000 meters (18.6 miles) when equipped with a
rocket-assisted projectile. The 8-inch was the most accurate in the Army
inventory. The M-110 was invented by a mistake with the wrong dimensions put
in the lands and grooves of the 8-inch tube. It worked so well during the
test that a round could be dropped in a 55-gallon drum 12 miles away after
the third shot and adjustment.
Q. What was the range of the M-107 175-mm
A. The M-107's combat experience with
the US military was almost entirely limited to the Vietnam War. There it
proved its effectiveness by having one of the longest ranges of any fielded
mobile artillery piece in the Cold war, able to launch a 147 lb (67 kg)
projectile out to 21 miles (33 km). This range advantage, along with the
ability to rapidly move from its last position, made it an effective weapon
for destroying enemy Command, Control, and Communications, and supply trains
behind the enemy lines while evading counter-battery fire against even the
longest-range Soviet counterparts, as was proven at Khe Sanh.
In service in RVN, the 175-mm SP gun was distinguished both by its long
range and by its inaccuracy at longer range. The gun was assigned to Corps
artillery units and a number of M-107/M-110 composite units were formed,
allowing the option of responding with the longer range M-107 or the more
accurate M-110. The tube on the M-107 required changing after approximately
300-400 rounds although later in the Vietnam war, new tubes with longer
lives were introduced.
Q. What was the rate of fire?
A. The M-110's rate of fire is 3
rounds per minute when at maximum, and 1 round per 2 minutes with sustained
fire and the M-107's rate of fire is 1 round per minute when at maximum, and
1 round per 2 minutes with sustained fire.
Q. What was the Time of Flight (TOF) for a
175-mm and an 8-inch projectile at maximum range?
A. Time of flight (TOF) is the
duration in which a projectile travels through the air from firing time to
denotation. TOF was influenced by many factors such as the angle of fire
(high or low), projectile weight (3, 4, or 5 square), and the charge used.
Other influencing factors included air temperature, wind speed, wind
direction, and air density. The rotation of the earth also influenced a
projectile in flight to some extent. The charge, projectile weight, powder
temperature, and tube wear influenced the velocity of the round as it left
the tube. A higher velocity meant a shorter TOF; conversely, a lower
velocity meant a longer TOF.
Q. What type of Ammo was used for the
A. Ammunition for the 8-inch included
High Explosive (HE), Controlled Fragmentation (COFRAM) and nuclear
projectiles. The COFRAM round (sometimes called firecracker or grenade
round) contained 108 bomblets that would be ejected by a Time Fuze which
would cause the bomblets to be ejected and spread and explode over a large
area in "bouncing-betty" fashion almost simultaneously. This round was very
effective against large groups of personnel.
High Explosive (HE) rounds could be fused with fuses Quick (commonly called
PD for Point Detonating and could be set to delay), Time (mechanical time)
and Variable Time (VT).
Nuclear rounds weighed 242 pounds. A nuclear 8-inch round was blue on the
bottom one-third and the top two-third was brass.
Q. What type of Ammo was used for the
A. Only High Explosive (HE)
projectiles were used on the 175-mm guns.
here for a
picture of an 8-inch and 175mm projectile (Courtesy of Dan O'Brien).
here for more specs on the 175mm projectile (Courtesy of Dennis
Q. What was the weight of the projectiles?
A. An 8-inch projectile weighed 200
lbs. and a 175-mm projectile weighed 147 lbs (Note: there are multiple
different sources on the 175-mm projectile weight. While most indicate 147 lbs,
some indicate 174 lbs but this is thought to be a typo or transposing of
numbers. Click here to see pages (in PDF
format) from the
Army Ammunition Technical Manual (courtesy of Bill Burke) for confirmation of
the 147 number. Click
here to view the full
Army Ammunition Technical Manual).
Q. Were all powder bags the same?
A. The powder bags were varied in
length, and numbered or might have been lettered, in order to maintain the
same start angle of tube, and using different bags to add or subtract the
distance of the called in fire mission. There was also a difference between
the High Explosive (HE) and nuclear powder bags, both in appearance and
composition. For more on the Propellant charge, click
(Courtesy of Dennis Blalock).
(Courtesy of Dennis Blalock)
"We called them zones 1, 2,and 3. When FDC said zone 1, we took 2, 3
from the charge and only loaded zone 1, or if FDC said zone 2, we used 1 &
2. If zone 3 we used 1,2,3, with a bore reducer jacket. The weight of zones
1, 2 & 3 was 58lbs (just the powder) , but container, powder, packing and
primer and all according to the manual was 96lbs"
8in howitzer (Courtesy of Dennis Blalock)
"If FDC said green bag charge 3 you only loaded green bag charges1, 2, 3
and you discarded 4, 5. If charge 6, you were told white bag charge 6 and
you loaded white bag charges 5 & 6 and you discarded 7
8in howitzer green bag is charge1 thru 5
8in howitzer white bag charge 5 thru 7
8in howitzer white bag charge 8"
Q. What determined how many powder bags
A. The number of bags to be used was
based primarily on the range to target and the angle of fire (low-angle or
For the 8-inch, there was two types of power bags, Green bag and White bag.
Green bags were numbered 1 through 5; White bags were numbered 5 through 7.
The number denotes the charge; the higher the number, the longer the range.
FDC determined the charge for indirect fire (aiming and firing without
relying on a direct line of sight between the gun and its target) primarily
based on the range to target. For direct fire (aiming and firing with a
direct line of sight between the gun and its target), they would use the
highest charge to get the maximum effect. The angle of fire (high-angle or
low-angle) also helped determine the charge, based on the range.
Notice the overlap in charge 5 (Green bag and White bag). A charge 5 White
bag was only used in an emergency, since once it was used, charges 6 and 7
were useless and had to be destroyed. There was also range overlap for each
adjacent charge. For example, you could hit certain ranges with either 1 or
2; 3 or 4, etc. The lowest charge possible was used to reduce wear and tear
on the howitzer (and the ears of the cannoneers).
Q. How long was the tube on the 175mm?
of Tom McNeight)
Q. How long was the tube on the 8-inch
of Tom McNeight)
"Found two references to
the 8” SP M110 having a barrel length of 25 calibers. Therefore 25 x 8” =
200 inches or 16.67 feet. I assume that includes the muzzle brake."
Q. How were the guns adjusted for the
A. The fine-tuning came into play by
slight addition or subtraction of tube angle to adjust for small distance
variation. The howitzer had a panoramic telescope with 6400 mils so
adjustments were in mills instead of degrees (360) to more fine-tune the
process. A Collimator replaced the aiming post in 1969, which looked like a
little telescope and had a light with many numbers it. FDC would give the
gunner one number to look for after the gun was laid, looking from one
telescope to another which further fine tuned the quadrant (up and down) as
well as the deflection (6400 mils).
Click here for information describing the use
of the Collimator and click
here for follow-up
information on this subject.
Q. What role did the Fire Direction Center
A. When a fire mission was received by
the firing battery from a forward observer, the Battery FDC contacted the
Battalion FDC who, in turn, would contact Division or Corps Artillery
Headquarters for permission to fire on the target. Once permission from
higher headquarters was received, both the Battery and Battalion FDC would
prepare firing data from the adjusting gun to the target. FDC’s data
included the direction to set the tube in mils, the quadrant (elevation plus
or minus the difference in altitude between the gun and target) the tube was
to be elevated, and the powder charge to be used in the mission. Once both
Battery and Battalion FDC’s agreed on the data, the information was sent to
the gun to fire on the target.
After the round hit in the target area, the FO (Forward Observer) or AO
(Aerial Observer) would adjust the impact of the following round by telling
the FDC to add or drop, and/or move the impact right or left. This procedure
would continue as the FDC’s refined the data to place the round on target.
When a round impacted within 50 meters of the target, the FO/AO would make a
final adjustment and request the unit Fire for Effect.
For observed fire, a forward observer (FO) or aerial observer (AO) would
send a fire mission to the FDC. The fire mission consisted of the target
location, type of target (e.g., personnel in the open, personnel in bunkers,
wheel vehicles, tanks, and the like), and the ‘attitude’ to the target. The
attitude was the direction to the target from the observer’s perspective.
The observer would also provide other information, such as “danger close” if
friendly troops were close to the target.
Using this information, the Fire Direction Officer (FDO) would issue a fire
order to the FDC. The fire order usually consisted of the type of shell and
fuse to use; the ‘base piece’ to use for adjustment; and the number of
rounds to fire during Fire-for-Effect (FFE). Using the data provided by the
observer and the fire order, the FDC entered the targeting information into
the Field Artillery Digital Automatic Computer (FADAC). The FADAC provided
the azimuth to target, deflection, quadrant, charge, and, if any, fuse
setting usually within 30 to 45 seconds. The FADAC was quick and accurate
provided it was setup properly and the targeting information was entered
As a manual backup, the FDC also plotted the targeting information on the
Horizontal Chart to determine the azimuth, range, and direction to the
target and on the map to determine the target altitude. Using the range and
direction to target, the FDC calculated the elevation and deflection. Using
the altitude, the FDC computed the ‘site’ to the target. When the FDC
computed the data manually, the FDC used a Graphical Site Table (GST) to
determine the elevation in mils to the target. A Site Table was used to
determine the ‘site’ in mils, which was used to compensate for any
difference in target altitude (height above or below the guns). The ‘site’
was added or subtracted from the GST elevation to determine the quadrant;
corrections were also applied to the deflection before fire commands were
sent to gun.
FDC would calculate the ballistic solution needed for a given target and
send fire commands to the “base piece.” In an 8-inch or 175-mm battery, the
base piece was either gun 3 or gun 4. In a 105-mm or 155-mm battery,
commands were sent to a platoon of guns, normally guns 3 and 4. Fire
commands consisted of the type of shell, fuse, charge, deflection, and
quadrant, and any special instructions. Once the gun reported “ready,” the
FDC sent the command to fire. For observed fire, the observer would send
target corrections to the FDC. FDC would recalculate the ballistic solution;
send new fire commands – usually a new deflection and quadrant - to the base
piece; and once ready, FDC would send the command to fire. This process
repeated itself until the rounds were on target. Once on target, an order
was given to Fire for Effect (FFE). During FFE, all guns fired one or more
volleys on the target using the same “data” and each gun reported “round
complete” when finished.
FDC used a special type of shell for ‘soft’ targets such as personnel in the
open called the “fire cracker” round. The firecracker round, controlled by a
time fuse, had 108 grenades (bomblets) inside the shell. The round was fired
at a high quadrant so that it would drop its ordinance about 400 meters
above the target. The back of the round would pop off and the 108 bomblets
would fall towards the ground. Each bomblet has a pair of metal wings that
would open to slow and control the fall. Once the bomblet struck the ground,
it would bounce up approximately 6 feet and explode. This was an extremely
lethal weapon in Viet Nam. One major consideration for the FDC was to ensure
this round was NOT fired near friendly troops because sometimes the bomblets
would get hung in dense foliage or not immediately detonate. Friendly troops
entering such an area might be harmed by unexploded ordinance.
The 8-inch and 175 mm howitzers had a max deflection of 533 mils left or
right. As a result, FDC would normally require the gun to lay on a different
azimuth if the deflection to target were greater than 400 mils left or
right. This was to reduce the strain on the gun’s carriage and hydraulic