The problems were at every level of tank operation and led to many crew members feeling that the tank ‘s performance and ability to fight suffered, feelings shared by high ranking armor corps officers and staff. Some of the problems were initially addressed during the Centurion’s early years of service by a host of minor, temporary and frequently inadequate modifications to some of the tanks. Amongst these early modifications, at least two significant upgrades were also completed in that period: the inclusion of the external rear hull fuel tank and the use of the British L7 105mm gun on some of the Centurions (for complete details on the early years of the Centurion in IDF service, see the first two parts of this series).
The main problem with the Centurion in IDF service was its petrol-fueled Meteor engine. This engine’s problems included a short service life, a lack of power resulting in a low power-to-weight ratio, the use of an extremely flammable fuel and its high petrol consumption rate, which resulted in an inadequate operational range. Solving the Centurion’s problems required extensive research in order to analyze the tank and its associated systems. The end result was a program that would convert the Centurion or, as it known in Israel, “Shot” (“Whip” in Hebrew), into an advanced tank with greater firepower and range, and with increased operational comfort for its crew and easier maintenance by its mechanics and ordnance staff.
This significant program was given to a special team within the Ordnance Corps. Lead by a very talented Army engineer, Colonel Israel Tilan, the head of the Tank Branch of the Ordnance Corps, the team also included Majors Ben-Zion Ben-Bassat, Moshe Keidar and Arieh Ramon along with IDF civilian employee Uri Yachin. In retrospect, it can be said that the Ordnance Corps met its goals and even exceeded many expectations. Their achievement was publicly honored in 1970 when the team was awarded the prestigious Israel Defense Prize for this project. It should be noted that a few years later Israel Tilan, having been promoted to Colonel, was also very actively involved in the development of the Merkava tank alongside General Israel Tal. As mentioned above, the primary problem with the Centurion was the ageing Meteor Mark 4B, a 650hp water-cooled, gasoline-fuelled engine and a suitable replacement was needed immediately. The team searched the world market for a more modern engine better suited to the needs of the IDF. The new engine had to meet the following requirements:
1 . Due to the urgency of the program, the new engine needed to be in production and available for immediate delivery and not in development
- The engine needed to be diesel fueled, because the fuel is less flammable and such engines have greater fuel efficiency
- The engine’s purchase must come with no political complications or restrictions
- The new engine must be similar in size to the Meteor engine to fit within the existing Centurion engine compartment
- The engine must be affordable, since the plan was to convert more than 1000 tanks over several years and the budget was limited
- The new engine must provide the specified power, speed and range performance
- Ease of maintenance was very important, especially in the field and under combat conditions with limited technical staff
- The new engine must be more reliable than the Meteor easier to change out under field conditions with a limited number of mechanics
- Local industry must participate in production or maintenance of the new engine
The plan was to start full production of the Shot Kal conversion at the beginning of 1968, but the project was postponed because of technical and bureaucratic problems and then delayed again due to the onset of the Six Day War. Although the war resulted in great victory for Israel over the 3 strongest enemy Arab states, Egypt, Syria and Jordan, the program continued to be delayed after the war because the Ordnance Corps was fully engaged with higher priority tasks. Returning the IDF Armor Corps to full combat readiness was at the top of that list, so no space or manpower was available to convert Centurions. When the Ordnance Corps was eventually ready to restart the project, the conversion program was further delayed by the reinstatement of the unofficial American weapons embargo that had been in place against Israel since 1948. Although the embargo had been weakening since the beginning of 1964, it was more strictly reinstated for several months after the war.
Long experience with the embargo had produced Israeli search and purchase teams that knew just how and where to buy weapons while under the sanctions and the first rule was; don’t waste time trying to go through the United States government, the best bet was to approach American producers directly to examine their products. The head of the Ordnance Corps and the main driving force behind the project, Colonel Amos Horev, visited different companies in the United States to investigate ordering engines. To start the process he presented them with the specification documents that outlined the IDF performance requirements for the new engines. After the first screening of potential candidates, several engines were acquired and tested but only three of them met most of the criteria; the Cummins diesel engine that was then being used to modernize the IDF’s M50 and M51 Sherman tanks, Teledyne Continental’s AVDS-1790-2A air cooled diesel engine and a water-cooled GM diesel engine that was being used at that time to upgrade Italian tanks. After additional trails that including building two prototypes powered by Cummins and Continental engines, the team selected the Teledyne Continental diesel engine. Producing 750 hp, it met most of the criteria, and performed the best in the test program. Although it was the most expensive choice, it had an additional and very significant advantage over others contenders, it was the same engine used in the newest tank in IDF arsenal, the M48A3, allowing standardization with that growing fleet of tanks. In addition, there were plans to upgrade older M48A1 and M48A2C tanks with the Continental engine.
With the limited budgets and manpower of the IDF, standardization was a huge advantage because it significantly reduced logistical issues like the stocking of replacement parts, as well easing the training of the technical staff and mechanics. The adoption of a diesel engine and especially the Continental diesel had many advantages over the gasoline-fed Meteor engine:
- Diesel engines are more durable, need less maintenance and have a longer time between overhauls
- Diesels are more fuel efficient, significantly increasing the Centurion’s range
- The increased power of the Continental engine significantly increased the power-to-weight ratio of the Centurion and it would no longer be considered underpowered
- The increase in power resulted in a significant increase in road speed to 45 km/h and in off-road speed to 17 km/h
- The higher power-to-weight ratio also allowed the Centurion climb 60 degree slopes
- The diesel engine had a significantly lower risk of fire during refueling operations or during engine warm-up
- The lower flammability of diesel fuel compared to gasoline meant that vehicle combat survivability was significantly enhanced after hits to the engine or fuel compartments
- It was possible to change Continental engines in the field in less than 2 hours compared to the 20 hours required for the Meteor engine
- Tank operations were less expensive due to the lower cost of diesel compared to gasoline
- Fuel handling logistics were safer and easier with diesel compared to gasoline
- Finally, because it was air cooled, the Continental engine did away with the Meteor’s liquid cooling system also eliminating the problems associated with radiators and leaking fluid lines
- Combined, these advantages of the Continental engine over the older Meteor greatly increased the operability and the survivability of the Centurion and its crew-members during the battles to come
Replacing the engine was only the first step in modernizing the Centurion. A further problem was the Meritt-Brown Z5IR gearbox. Many IDF Centurion drivers complained about its poor performance. It was very tiring for the driver to have to be continuously changing through the gear train working the transmission’s problematic clutch especially while trying to negotiate the rocky ground of the Golan Heights or during combat operations. The most logical solution was to use the same transmission that was paired to the Teledyne Continental AVDS-1790-2A in the IDF’s M48A3 tanks and so the Allison CD-850-6 automatic transmission was chosen to replace the Centurion’s original Meritt-Brown gearbox.
After the conversions, the life of the IDF’s Centurion drivers changed completely and it was as if they were suddenly driving American civilian automobiles after having struggled with a British heavy track from the 1940s. Not only did the choice of the Allison transmission increase standardization in the logistical train, but the standardization of driver and mechanic training across several vehicle types increased manpower flexibility and reduced overall operating costs even further. Finally, and perhaps most importantly, the reduced workload that the new transmission imposed on the driver meant reduced fatigue, a key factor in the middle of demanding battle situations.
In addition to changing the engine, the air filtration system was changed to handle the harsh, dusty conditions of the Negev and Sinai deserts. The design team continued to standardize on M48 systems and chose the Donaldson box air filters to be installed on the fenders on either side of the hull, similar to their installation on the M48A3. The system was hermetically sealed to prevent damage by the heavy dust in these harsh environments. Testing confirmed that the new filters were more durable than the older British system. Even though the power pack and filter systems were an existing and proven system, there was still a need for many changes to the power pack so it would fit within the existing Centurion engine compartment. More than 300 changes were made in collaboration with the Teledyne engineers in the USA after a Centurion tank was cut apart and a full-scale engine compartment was specially built and supplied to the factory from Israel to allow exact placement of the new power pack components.
After months creating the modifications to the Centurion and after more than two years of planning and the preparation of more than a thousand blueprints, it was time to fit the new power pack into a tank in Israel. Everything fit perfectly, but when it came time to put the transmission into first gear, it was discovered that the system wanted to go in reverse! The cause of the problem was quickly discovered, it turned out that the orientation of the engine in the new power pack was rotated 180* to the original Meteor engine, the implications of which were not appreciated before the embarrassing final integration tests. Major Tillan immediately took full responsibility for this embarrassing mistake and, together with Colonel Amos Horev, the head of Ordnance Corps quickly developed the simple solution of adding an additional idler gear to reverse the shaft rotation. This was another example of Major Tillan ‘s fine leadership, instead of blaming others or making excuses, he took the responsibility onto himself as the head of the project.
In total, more than 2000 new parts were incorporated in the Shot Kal conversion, starting from simple bolts and finishing with the new engine. Half of the parts were produced or bought from local suppliers, and gave additional confidence to the Israeli military vehicle industry in their now-proven ability to cast armor and produce other complicated parts. The rest of the parts were ordered from the US, and were mainly the components related to the engine, gearbox and filters. The orders were placed with the US-based factories in the form of upgrade kits for the engines and gear boxes, and they were similar to kits that were used in the programs to upgrade the earlier M48 tanks like M48A1 and M48A2C to the M48A3 standard in USA as well as Israel. The Shot Kal program provided important experience that, in the end, helped make possible the first Israeli designed and produced main battle tank, the Merkava.
As a result of all the delays, the conversion production line only officially started in the first weeks of 1970, around two years later than planned and, even then, the initial work on the tanks did not include the power packs. Just as Israel was starting the Shot Kal conversion program, it was also running a parallel program to upgrade their early M48 versions to the new M48A3 configuration. The huge numbers of engines needed for the Shot Kal project created engine availability problems when the conversion line finally started. It was hard for the American factories to produce so many engines in so short a time especially when these engines were also needed for the production of new American M48A3 tanks as well as for replacements for the operational battalions in Europe and in Vietnam.
As with the previous Sherman M50 and M51 projects, the original Centurion tanks were stripped down to the hull shell which was then modified and extended to allow addition of another external fuel tank to the rear of the hull.
The remainder of the tank was rebuilt incorporating many new parts that were more efficient, modem and also more economical than the original parts. These modifications were the result of the lessons learned since the introduction of the Centurion into service in the IDF: countless lessons learned from practice drills, combat incidents, and, of course, lessons from the Six Day War itself, in which the Centurion had mainly participated in the Central and South Commands and been the spearhead of the Israeli armored brigades. In addition, many modifications originated from requests from the ordinary crewmen who operated the tanks as well as from the wishes of their commanding officers and the technical support teams. The fighting compartment was totally changed in addition to the work being done in the engine compartment.
The Shot Kal conversion also included the replacement of the original 20 pdr gun with the excellent British 105mm L7 gun, named Shrir (Muscle) by the Israelis, that was being produced under license in Israel. As the same modification had already been performed prior to the Six Day War, this part of the program was straight forward but additional enhancements were included in the Shot Kal program. This time the entire fighting compartment was arranged to enhance combat efficiency. The number of rounds carried was increased to 72, the number of ready rounds was increased, ammunition stowage was better protected and better arranged, eliminating the need to rotate the turret to access the stowed ammunition.
There were other major/minor modifications that had been introduced in previous IDF Centurion improvement programs and these were also added to Shot Kal tanks.