International Defense Review
March 1, 2001
SECTION: EQUIPMENT PROFILE; Vol. 34; No. 3
LENGTH: 4574 words
HEADLINE: M109 - modernizing for the millennium
BYLINE: SCOTT R GOURLEY
With about 6,000 systems in international service, the M109 self-
propelled howitzer is a familiar presence in global ground force
inventories. Originally introduced to US Army ground forces in 1963,
it was based on a 1950s design that in its M108 version incorporated
a 105mm cannon with an 11km range, or in its M109 iteration a 23
caliber-length 155mm tube that provided maximum ranges of 15km
(unassisted) and 20km (assisted).
The 'basic' (M109A0) model was followed in US inventories by the
1973 introduction of the M109A1, which featured a 39 caliber-length
cannon (M185) that extended maximum projectile delivery range to
18km, or to 24km when firing the M549 rocket assisted projectile
(RAP). The year 1978 saw the introduction of two new models: the
new-build M109A2 and the M109A3, an M109A1 upgraded to M109A2
standard. Both models introduced a range of safety and
The early 1990s saw the introduction of two additional models: the
M109A4 and the M109A5. The M109A4 program involved installation of
approximately 1,000 nuclear, biological, and chemical/ reliability,
availability, and maintainability (NBC/RAM) upgrade kits that were
assembled, packaged, and delivered to the
US Army by Barnes & Reinecke, Inc (BRI). The M109A5 also introduced
a new cannon (M284 cannon assembly with M182 gun mount) that further
extended the firing range to 30km, using the M549 RAP in conjunction
with the M203 charge (NATO Zone 8).
Around the world, the US M109 upgrade pathway has been accompanied
by a range of parallel upgrade programs conducted on various
international howitzer fleets. As in the US example, international
upgrades have generally focused on the introduction of new ordnance
and vehicle technologies, designed to extend range, improve
reliability, and enhance overall system survivability.
One representative international example can be seen in the mid-
1990s upgrade of 96 Spanish M109 systems to a newly-designated
M109A5Espana (M109A5E) configuration.
The initial phase of the M109A5E upgrade program involved the
physical survey of 96 existing Spanish Army M109 systems located at
multiple sites throughout Spain. This survey, which was co-ordinated
by the US Army Security Assistance Command (USASAC) and designed to
identify the 'baseline configuration' for the Spanish howitzer
fleet, was conducted by a team consisting of BRI personnel, Spanish
Army representatives, and representatives from the US Army's
Armament and Chemical Acquisition and Logistics Activity (ACALA),
located at Rock Island, Illinois.
In addition to three different M109 configurations in the Spanish
Army fleet, survey team members held discussions with howitzer crews
and system maintenance personnel in an effort to identify any unique
operational characteristics of the Spanish M109s. Based on this
survey information, the team assembled a single M109A5E upgrade
package that BRI representatives highlight for "[eliminating] the
kit redundancies and costs necessary in a sequential upgrade (M109
to M109A1 to M109A3 to M109A4/A5)".
A prototype transformation process focused on development of the
upgrade kit and upgrade instructions specifically created for the
Spanish Army depot facility in Segovia, Spain. Completion of the
prototype upgrade was followed by a Spanish government request for
an additional 93 system kits, each kit containing more than 1,100
individual items. At about the same time, Spanish representatives
also decided to incorporate the improved M284 155mm cannon and
associated components in the overall M109A5E package. The cannon
change mandated expanded USASAC co-ordination of Letterkenny Army
Depot for refurbished turrets, Rock Island Arsenal for gun mount
modifications, and Watervliet Arsenal for production of M284
cannons. The resulting 93 M109A5E upgrade kits were delivered to
Spain by BRI at the end of October 1996.
Other recent international M109 modification activities have
featured the installation of a modification kit developed by
Rheinmetall Landsysteme GmbH. Originally developed to meet the needs
of the German Army, the Rheinmetall upgrade featured installation of
a new 39-caliber 155mm barrel that increased the range of the new
M109A3G configuration from 18.6km to 24km firing unassisted L15
projectiles and to 31km with base-bleed projectiles. Upgrade of the
German M109s was also followed by the installation of the
Rheinmetall 39-caliber barrel in the Norwegian Army's M109s.
In addition to such 'pure upgrade' programs, some international M109
modernization packages are developed and fielded as a combination of
upgrades to existing systems combined with new system acquisitions.
An example of this can be found in the 1990s Austrian M109A5Oe
During the period 1992-95, United Defense LP developed a prototype
vehicle and technical data package for the Austrian M109A5Oe
variant. This development process was followed by the manufacture of
54 'new build' M109A5Oe systems at United Defense facilities in
York, Pennsylvania, during 1995-97, and the subsequent delivery of
an additional 125 upgrade kits for in-country modernization of ex-
British Army M109A2/A3s to M109A5Oe configuration in the1997-2000
According to the Austrian program director, Dr F Felberbauer, the
user's key demands for the M109A5Oe were a 30km range, improved
responsiveness, 'shoot-and-scoot' and autonomous operations
capability, and the ability to fire newer generations of projectile.
It was decided a 39-caliber cannon should be retained because, in
the Austrian view, 52-caliber tubes are too long for maneuvering in
Alpine villages (and 47-caliber tubes marginal for the same reason).
In order still to achieve the required full 30km range, the Austrian
Army is using 47kg ERFB Base Bleed projectiles in combination with a
Swiss Zone 8 charge modified by Nitrochemie with a special increment
(also referred to as 'Zone 8.9'). An unexpected bonus with some of
the M109s acquired from the UK, was that the angle of the forcing
cones of their M185 cannon had already been modified by Royal
Ordnance to be able to fire higher pressure charges (NATO Zone 8),
obviating the need to fit the uprated M284 cannon.
Other items incorporated by the Austrians included an APU for
training purposes; an enhanced Swiss electrical system and 16-
channel slip ring to improve traverse capability (according to
Felberbauer with the previous drives, it had not been possible to
traverse the turret at cant angles greater than 3); a NAPOS
navigation and position system (that automatically switches from
navigating mode to ballistic mode when the powered travel lock is
unclamped from the barrel); and a Intertechnik rammer.
Today's M109 user faces a dizzying array of system upgrade
alternatives ranging from the enhancement of individual operating
characteristics to a revolutionary change in overall system
character. In addition, upgrade alternatives are offered in a range
of production/co-production arrangements performed by a number of
competing industry sources. Moreover, new manufacturers are
continuing to enter the M109 upgrade market on a regular basis.
South Africa's LIW is one of the recent arrivals on the M109 upgrade
market. In response to a United Arab Emirates (UAE) desire to
standardize critical component upgrades between its G6 and M109
howitzers, LIW is currently conducting its initial M109 upgrade
program, which it began in the fall of 2000.
The first LIW contract reportedly covers the supply and integration
of existing M109 position and navigation subsystems with a new
Kentron fire-control system. Instead of the older optical dial
sights - subsystems that mandated the physical 'laying' of firing
units through mechanical survey processes - LIW is equipping the
M109s with dual (inertial and Global Positioning System [GPS])
position/navigation sensors. The sensor combination provides ring
laser gyroscope-based gun laying accuracy to within 1mil, an onboard
accuracy that translates to the ability to conduct fire missions
immediately after arrival at a firing position. The positioning
systems are further linked to a weapon management system computer
for receipt of firing data as well as a projectile muzzle velocity
radar that will measure and store projectile velocities and other
data, further increasing system accuracy.
Additional LIW M109 upgrade activities include modification and
installation of a remotely-operated barrel travel lock, installation
of a semi-automatic hydraulic push rammer, and installation of an
auxiliary power unit in the rear of the turret to power all turret
subsystems, including a new air-conditioning unit.
With more than 30 years of experience in complete and partial
overhaul programs for a range of M109 series howitzers, Netherlands
company RDM Technology, BV offers a flexible range of upgrade
options. Pointing to an experience founded on licensed M109
production starting in the 1960s and running through the 1980s,
company program descriptions highlight a range of continuing
upgrades conducted through the 1980s and 1990s. Recent program
examples include the overhaul of 30 Canadian M109s, the upgrade of
126 systems for the Netherlands, and the further upgrade of 85
former Netherlands Army M109s to an M109L47 standard for the UAE.
Beginning in 1997, the company started the development of what it
terms "the ultimate upgrade of the M109", that includes installation
of a new 52-caliber long-range barrel. Firing trials of the new 52-
caliber design, known as the M109-2000 Technology Demonstrator,
started in late 2000 and continue at this time.
In addition to the new 52-caliber cannon, the M109-2000 includes a
range of enhanced subsystems like the Intertechnik flick rammer and
Rheinmetall Landsysteme GmbH (previously KUKA Wehrtechnik GmbH)
ammunition handling kit (the ammunition handling kit has also been
ordered for the German Army's M109A3G systems noted earlier).
Taken together, RDM offers a spectrum of flexible upgrade
alternatives under the umbrella title of "M109 Howitzer Improvement
Program (HIP)". Company descriptions note that the M109 HIP "aims at
an extension of the howitzer's lifetime by introducing newly
designed systems and components to provide the howitzer with the
necessary firepower and other features nowadays required in modern
theaters. The Improvement Program is accomplished by using only
existing and proven systems and components and can be adjusted in
accordance with the customer's wishes.
Apart from qualifying the individual components, the improved
howitzer has been qualified with all the additional features
integrated in the howitzer. The results of these tests have clearly
shown that the basic system is perfectly capable of absorbing the
effects of the various added systems to the basic system, including
the upgrading with long range 47-caliber and 52-caliber guns."
HIP program upgrades include items like a remotely-controlled barrel
travel lock, enhanced navigation and fire-control systems, automatic
or semi-automatic loading options, and a new cannon - in 39, 47, or
52 caliber-length options - to provide increased range.
Additional new components include: NBC subsystem, hydraulic
subsystem; charge racks; ballistic cover; driver's night sight;
recuperator cylinder; auxiliary power unit; air conditioning unit;
an automatic explosion detection/fire suppression subsystem; and an
M109L47 engine upgrade kit.
In clarifying some of the different company upgrade options and
'marketing designations' that have been assigned to RDM's various
M109 enhancement activities, Hans Blaauw, General Manager for
Marketing and Sales, notes that "RDM has been active in development
of M109 upgrades and improvements over the past 15 years, in the
mean time, several names have come up for different M109 upgrade
"RDM has developed a modular M109 improvement package consisting of
some 30 different improvements and upgrades from which a customer
can choose, based upon his own priorities and available budget," he
adds. The ballistic upgrade possibilities RDM offers in place of the
baseline M185 39-caliber barrel include a new 39-caliber gun,
comparable to the M284 (able to fire NATO Zone 8 charges), a 47-
caliber gun (as supplied by RDM to the UAE Armed Forces), and "a 52-
caliber gun NATO standard", fabricated by Royal Ordnance. Blaauw
describes the 47-caliber gun as "according to the Joint Ballistic
Memorandum Of Understanding [JBMOU] but not NATO standard".
(According to Blaauw, its 21-liter chamber gives the L47 the same
muzzle velocity for a given projectile/charge combination as the 39
and 52-caliber barrels. Therefore, despite the fact that 47 caliber
is not supported by NATO, the NATO firing tables can be used for the
L47 without modification.)
"The M109-2000 represents the ultimate upgrade using all of the
remaining upgrade potential within the M109. It consists of the 52-
caliber gun upgrade and all the other modular improvements we have.
This has been built into our M109-2000 Technology Demonstrator to
prove its functionality. The M109-2000 has an improved firing range
[40km with M864/DM652 base bleed], rate of fire [burst three rounds
10s/nine rounds in 54s] and improved accuracy.
The M109 can be used in autonomous roles and has 'shoot-and-scoot'
capabilities. It is interoperable with modern ammunition and charge
systems and within a modern digital battlefield. Also crew safety,
ergonomics, environmental aspects, survivability, availability,
reliability, maintainability and operational cost are improved. The
last aspect has been mainly achieved by reducing the M109's crew
from 6 to 4 persons. RDM's modular upgrade program offers a
performance comparable to new modern SP guns for a fraction of the
cost," he says.
In terms of specific program designations, Blaauw summarizes that
"Other names for our M109 variants are certain versions where a
customer or potential customer selects a combination of different
elements of the modular upgrade package. The M109L47 is the system
we supplied to the UAE, consisting of a 47-caliber gun upgrade, a
semi-automatic projectile loader, remotely controlled travel-lock
and some six other options.
The M109A5++ is a configuration in which the A2/A3 version is
upgraded to A4/A5 with the standard US RAM-PIP kit. The first + is
because instead of the M284 gun in the A5 we install the L52 gun
which gives 10km more range. The second + is for the installation of
several systems that are not normally included in the M109A5, such
as a semi-automatic projectile loader and a navigation and fire
Another company offering a variety of M109 upgrade alternatives is
SW Thun (formerly SW Swiss Ordnance Enterprise Corporation). As one
of several international M109 upgrade providers, SW Thun has
developed a package of modular system enhancements focused on
firepower, reliability/maintainability, and survivability.
Firepower enhancements stem from the installation of a new 47-
caliber armament system. With more than 400 cannons already ordered,
the L47 Swiss type-classified cannon system fires all NATO standard
ammunition at ranges up to 36km. (The combination of the Nitrochemie
Zone 9 charge and the 47-caliber gun increases the range of older
projectiles, including the M107 to 25km and of base-bleed cargo
rounds to approximately 36km).
In addition, its fully chrome-plated bore eliminates barrel erosion
and helps guarantee constant muzzle velocities with no range loss or
increased dispersion zone during the entire life span of the barrel.
Other barrel design features reportedly include 60-groove rifling
with reduced rifling angle to permit firing of the older projectiles
(viz the M107) with Zone 9 charges. Coupling the cannon with a semi-
automatic loading system, together with increased onboard stowage of
40 rounds and 64 charges, also supports higher firing rates for the
Reliability and maintainability enhancements include a new
electrical system (with a 16-channel slip ring) and fault-finding
diagnostics. Numerous survivability features in the Swiss upgrade
design include: enhanced tactical flexibility through the use of a
new navigation/positioning system to facilitate first-round
delivery, and 'shoot-and-scoot' options through a remotely operated
travel lock; driver night vision enhancements; plus fire
extinguishing systems in both crew and engine compartments. The
upgrade also further enhances crew survivability with design
features including blast-proof sliding door separation between the
crew compartment and the propellant magazine and additional magazine
compartment pressure-relief features.
The latest M109 upgrade configuration to enter US Army inventories
is the M109A6 Paladin. As with earlier models of the M109 system,
the M109A6 Paladin 155mm self-propelled howitzer provides the
primary indirect-fire support to heavy divisions and armored cavalry
regiments. The enhanced Paladin configuration is achieved through
extensive modifications to existing M109-series vehicle hulls and
the subsequent introduction of an entirely new turret structure.
Some of the new or enhanced subsystems incorporated in the Paladin
upgrade include an onboard ballistic computer and navigation system,
secure radio communications, a modified 39-caliber M284 cannon with
improved M182A1 gun mount, automatic gun positioning, automotive
improvements, improved ballistic and NBC protection, driver's night-
vision capability and built-in test equipment. Additional chassis
upgrades include a remotely actuated travel lock (for quicker
emplacement and displacement), longer torsion bars (to help support
the new turret) and a low heat-rejection engine with improved
Described by US service representatives as "the first digitized
combat vehicle in the US Army's inventory," Paladin has
significantly improved responsiveness, survivability, lethality and
reliability compared to the earliest M109s. Like the M109A5, it uses
the M284 cannon which is an enhanced version of the M185 with a
modified torque key to allow use of the M203 charge, but in addition
it has a new cab with improved protection, and the Honeywell
Automated Fire Control System (AFCS) which gives it its autonomous
The first 164 Army Paladin systems were manufactured under a
September 1991 Low Rate Initial Production (LRIP) contract that
resulted in First Unit Equipped (FUE) status in April 1993. A
subsequent full-scale production (FSP) multiyear contract covered
630 howitzer conversions, with additional options for 83 systems and
a follow-on order for 73 more Paladins, bringing the total number of
units produced under FSP to 786. The final vehicle conversion
contracted under this series of contracts was delivered to the US
Army in late June 1999 (164 LRIP + 786 FSP = 950 M109A6s currently
in US Army service).
M109A6 Paladin conversions through the middle of 1999 were conducted
by United Defense's Paladin Production Division (PPD), established
on Letterkenny Army Depot (LEAD) property. The physical location
facilitated the establishment of a 'Paladin Enterprise' workshare
agreement between the depot and United Defense.
Following receipt of their 950th M109A6, US Army fleet planners
indicated that a portion of the army's remaining M109 howitzer
inventory would receive the M109A5 upgrade, which includes some
automotive and crew NBC protection improvements and Paladin's M284
cannon and M182A1 gun mount. In addition, Army National Guard
planners revealed ongoing efforts to seek funding for additional
One result of those efforts could be seen in a Fiscal Year 2000
United Defense contract for the upgrade/manufacture of seven
additional M109A6 Paladins for Army National Guard units. The US$8.3
million contract, which was awarded by the US Army's Tank-automotive
and Armaments Command (TACOM), marked a significant milestone in the
M109A6 upgrade program since it reflected the first order for the
remanufacture of existing M109A5 systems into M109A6 Paladin
configuration since closure of the PPD that had been located at
Letterkenny and the official transfer of army depot responsibilities
for self-propelled howitzers from LEAD to Anniston Army Depot
(ANAD). Recent schedules reflect deliveries of the seven newly
upgraded systems beginning in November 2001 and continuing through
According to company spokesman Herb Muktarian, United Defense
contract activities are being conducted in York, Pennsylvania and in
Aiken, South Carolina. "Anniston Army Depot has a key role in the
project by doing the tear-down of the inducted M109A5s," he says.
"They are going to work on the new vehicle chassis: structurally
modifying the hull for the M109A6 configuration; and integrating
components like a new engine and other new subsystems so that the
vehicle has 'zero miles/zero hours' when it comes out of Anniston.
Essentially it's a new chassis that will then come up to York where
we are going to manufacture and assemble brand new cabs [turrets]
and then integrate the turret to the chassis for final testing in
As a spin-off to United Defense's M109A6 engineering development
activities, the company has for several years been marketing an
"export only" M109 upgrade package, which it now calls the
International Howitzer (the initial target customer was Kuwait - Ed,
see IDR 5/1999, p62).
The International Howitzer utilizes the same turret structure
developed and fielded for the M109A6 Paladin. Designed to meet the
higher firing loads of extended range ordnance, the cab structure
houses a 52-caliber modified M284 155mm cannon supported in a
modified M182A1 gun mount. The 52-caliber ordnance, which includes
fume extractor and double baffle muzzlebrake, is built by Watervliet
Arsenal and is extended-range JBMOU compliant.
The ammunition loading design configuration provides International
Howitzer with maximum firing rates up to three rounds in 15s and six
rounds per minute, with optional semi-automatic loading system and
laser ignition system or automatic primer feeder. The system has
onboard carrying capacity for 39 complete rounds. The power pack is
the same as that found on the M109A6 with the suspension upgraded to
handle the higher firing loads.
"The International Howitzer includes all the enhancements of the
M109A6 Paladin system and also provides a 52-caliber 155mm cannon
with improved rate of fire," explains David Phillips, Director of
Artillery Programs for United Defense's Ground Systems Division.
"This commonality, from our perspective, means that the
International Howitzer is an operationally-capable and logistically-
supportable M109 upgrade package."
He adds that "our International Howitzer provides a new turret
design structure that is common to the M109A6, and that turret
design structure was designed specifically for the increased loads
of a longer caliber-length cannon and extended-range ammunition. And
that separates what we're offering from any other M109 upgrade on
the international market. That's a clear discriminator. Clearly the
design for the Paladin and the International Howitzer addresses the
loads seen from extended-range armament, whereas the other
international M109 upgrades have not addressed those loads into a
redesign of the turret structure."
Noting that "the design for Paladin addressed extended-range
ordnance", Phillips adds that "from our standpoint, the smaller
turret on the original M109 was designed to carry a 23-caliber
cannon. And then that evolved through the M109A5 with increases in
cannon lethality that led to a 39-caliber system. The Paladin was
the first to address the impact of extended-range capabilities
through a complete redesign of the turret structure."
Adam Zarfoss, United Defense Program Director for Paladin and
International Howitzer, says: "The Paladin upgrade addresses system-
level improvements to the M109. During the development of the
Paladin, it was determined that the old cab structure would not
withstand the higher firing loads of extended-range ordnance over
long periods of time. And the US Army designs everything for
infinite fatigue life."
In addition to the new cab structure, Phillips cites a second major
discriminator based on Paladin's production history. "We are the
M109 OEM [Original Equipment Manufacturer] and United Defense has
used that new turret design on all 950 Paladins built to date as
well as the seven that are currently under contract. And we've done
that through co-operative co-production with the US Army depot
system. And that's a program that really establishes a validated
model for structuring a co-production program."
Although declining to identify specific customer interest, United
Defense representatives cite International Howitzer program interest
from countries in the Middle East, Far East and Europe. They add
that a pre-production prototype system has been developed and
initial deliveries of upgraded International Howitzers could begin
within 24 months of contract start.
In addition to offering the domestic M109A6 and the export
International Howitzer, Phillips adds that "United Defense stands
ready to offer a full range of M109 enhancements - everything from
M109A2 overhauls to A4 and A5 upgrades."
He goes on to note that United Defense's expertise in flexible
upgrade packages received two significant boosts with the company's
recent acquisition of BRI and Bofors Defence. "From the early 70s
and through even today, BRI has had the US government contract for
M109A2 through the M109A5 System Technical Support [STS]," adds
Phillips. "So, with their customer at TACOM Rock Island, they
control the technical data package for the earlier version M109s.
With the acquisition of BRI, United Defense is clearly the M109
Beginning with a basic design that started on paper in the late
1950s, the M109 self-propelled howitzer is entering its fifth decade
of military service as a vital member of ground force inventories
around the world. As such, the M109 series howitzer has few peers in
the world of combat systems. One major reason for the M109's
continuing viability is the wealth of upgrades that have been
applied or are available from multiple sources around the world.
Modern versions routinely deliver ordnance at twice the original
M109's 15km maximum range with the latest technology and marketing
demonstrators now reaching out to 40km. Likewise, artillery crewmen
who served on early versions would hardly recognize today's
automated and computerized cab designs with their multiple enhanced