M-110 8-inch Self-Propelled Howitzer and M-107 175-mm Self-Propelled Gun

 
 
The M-110 8-inch (203 mm) self-propelled howitzer first entered service with the US Army in 1963 and was the largest self-propelled howitzer in the United States Army's inventory. The M-110 was a “Howitzer” (low velocity, high trajectory, short range). The vehicle itself transports only two projectiles and five men, while the remainder of the ammunition and the crew is on board a tracked M-548. The M-548 was used in Vietnam as an ammo carrier in support of armored units or artillery.

The M-107 175-mm self-propelled gun (the last self-propelled “Gun” (high velocity, low trajectory, long range) in the U.S. Army inventory) and the M-110 8-inch howitzer had identical carriages but different tubes. The 175-mm. gun fired a 147-pound projectile almost 33 kilometers (20.5 miles). This impressive range made it a valuable weapon for providing an umbrella of protection over large areas. The 8-inch howitzer fired a 200-pound projectile almost 17 kilometers (10.5 miles), plus being the most accurate weapon in the field artillery. The 8-inch howitzer was found with most division artilleries, and both the 8-inch howitzer and 175-mm. gun were with field force artillery. At field force, the proportion of 8-inch and 175-mm. weapons varied. Since the weapons had identical carriages, the common practice was to install those tubes that best met the current tactical needs. One day a battery might be 175-mm; a few days later, it might be half 175-mm and half 8-inch.

Designed to be part of a common family of weapons utilizing the same chassis components, the M-107 and M-110 were essentially the same vehicle mounting different barrels. The hull of the M-110 is identical to that of the M-107 and is made of all-welded armor and high-tensile alloy steel with the driver at the front of the hull on the left, the engine to his right and the main armament at the rear. It features five road wheels on either side of the chassis with idler arms attached to torsion bars, with the track driven from the front by a 450 hp General Motors turbo supercharged diesel.

Click here for an article on the M-107 that is on the website of the Army Historical Foundation.

It was also possible to mount a wrecker boom on the same chassis to change tubes and pull engines. Another vehicle that was used for changing barrels was the…

M-578 Light Armored Recovery Vehicle (VTR)

The M-107 and the M-110 were both characterized by rapid barrel wear and the need to be able to change the barrels frequently and simply. The US Army developed a crane for this purpose based on the same tracked vehicle as the guns themselves. It has a turret with a boom rather than a gun barrel, and a winch, which gave it a recovery as well as a lifting potential. This equipment, the M-578, was issued to those artillery units using the guns during the 1970s. When the guns were withdrawn from service the M-578 was redesignated a Light Armored Recovery Vehicle, used to recover damaged vehicles from the battlefield. The hydraulic crane is housed in a turret mounted at the rear of the chassis. A stabilizing spade hydraulically lowers from the rear.

Click here to see an M-578 (link courtesy of Dan O'Brien 1/83rd)

There is a considerable amount of technical information on the 8-inch howitzer and 175-mm gun on the following website:

15th Field Artillery Regiment
 

Following are some Frequently Asked Questions.


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 men,
• 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 was moved?

A. There is only room inside for driver.

Q. How long did it take to set up after a move?

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 howitzer?

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 gun?

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 8-inch?

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 175-mm?

A. Only High Explosive (HE) projectiles were used on the 175-mm guns.

Click here for a picture of an 8-inch and 175mm projectile (Courtesy of Dan O'Brien).

Click here and here for more specs on the 175mm projectile (Courtesy of Dennis Blalock).

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 here (Courtesy of Dennis Blalock).

175mm Gun (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 were used?

A. The number of bags to be used was based primarily on the range to target and the angle of fire (low-angle or high-angle).

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?

A. (Courtesy of Tom McNeight)

"Regarding length of the barrel. Both Wikipedia and Military-Today.com state the length of the barrel is 60 Calibers. Caliber in tube length is a derivative of Navy guns. To arrive at the length in inches you multiply the bore in inches by the caliber. So 175 mm converts to 6.88976 inches: therefore 6.88976 x 60 calibers = 413.3856 inches or 34.4488 feet.

http://www.military-today.com/artillery/m107.htm

I have found other historical references like the one below “The Big Guns of Camp Carrol” which state the length of the 175mm barrel at 34 feet – validating the calculation above.

http://msuweb.montclair.edu/~furrg/Vietnam/brushcampcarroll.html

I have found another length of the entire gun on the 2/94 website. It gives the length of the “tube” as 413 inches (60 calibers) – as my calculation; but gives the length of the “cannon” as 35’ 8”. I think the tube length is probably correct. If I recall correctly, which might a stretch at this age, there was about another 2-3 feet behind the breech (refer to attached photo) to the back of the carriage that may account for the difference between 34 feet and 36 feet. So I think the 35’ 8” probably refers to the back of the carriage and the 36’ 11” refers to the back of the spade."

http://www.2ndbattalion94thartillery.com/Chas/175mm.htm

Q. How long was the tube on the 8-inch howitzer?

A. (Courtesy 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."

http://www.military-today.com/artillery/m110.htm

Q. How were the guns adjusted for the target?

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 (FDC) play?

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 correctly.

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 systems.

Click here to see a video of a 175mm being loaded and fired.
(Link provided by Dan O'Brien)

 

 

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