WHY IN THE WORLD WOULD ANYONE

BUILD A TURRETLESS TANK?

 9756 hits on target since 1998-04-13

The idea and basic concept of the "S" was presented by Sven Berge to the royal department of war materiel in august 1956. Studies and investigation had been conducted for three years by then. These included study of hit- and damageassessment from WWII aquired from the british in 1954. More than 2000 books and magazines on the reactions and injuries of tank crews as well as damage to hit tanks in actual combat were studied. These showed a high percentage of disabled tanks due to damaged turrets and gun controls as well as the fact that very few hits were scored below one meters height. They also showed that the risk of a hit per presented target area increased with height and that it was about 100% higher in the turret compared to the chassi. This led to the idea of mounting the turret directly on the tracks (or if you prefer, mounting the gun in the chassi). This would allow a low silouette with good protection in relation to weight. The Strv 103 was to be 25% lower that contemporary tanks. The target area became 25% less and in fire position 50% less (Soldat und Technik 7/82).

This meant that the gun would have to aimed by swiveling the entire chassi through track movement. This was in itself nothing new. It had been done by the french Char 1B in 1940 to aim its 75 mm gun. Gun elevation was not considered a problem if hydropneumatic suspension was used. The concept made an autoloader feasable and relatively simple. The need of a loader was eliminated and two tons of weight saved. The amunition for the main gun was to be stowed in magazines in the lower rear of the vehicle were they would be best protected. Contemporary tanks only had a portion of the amunition stowed to be used without redistribution which limits the firepower that can be immidietly delivered on target. It also made these tanks vulnarable to turret hits. The Strv 103 had no need for inner space to elevate or depress the main gun which allowed a compact design. Driving and aiming would be operations of similar kind which would make it possible to have one operator perform both of these functions with the same controls. The tank commander would have duplicate controls allowing him to immidietly take over and drive or aim the gun if the need would arise. In hasty situations the fire command would become uneccecary. The tank could actually be crewed by one man only in a pinch. The original idea called for a two man crew, but this came under fire from experienced tankers and tank instructors. A third man was added and this increased weight by two tons from the planned thirty.

The wooden mock up. Note the 20 mm autocannon.

Another advantage with the basic concept was the possibility of mounting a floatation screen on the chassi. It could even be permanently mounted. This meant that Strv 103 was the only tank that could traverse water with its own carried equipment regardless of depth. It was decided to do so. The research fascility of the defence had conducted a study on tank duels. It had also performed a number of test firings against different protective arrangements and armorplates with different angles and thickness. Effect behind armor was noted. With factors such as gun dispersion, range and target area, accuracy estimations was calculated. Factors like armor thickness and angles coupled to the effect of different anti tank rounds gave penetrention estimates. These were then used to calculate the probability of "victory" considering who fired first and rate of fire. The results highlighted the importance of a small target area, good frontal protection and duplication in vital functions in order to fire first. A studygroup was appointed to study three different alternatives.

  1. Altenative A. The trend in anglo-american tank development towards tanks in the 50 ton class with good protection but average mobility.

  2. Alternative T. The trend in french-german tankdevelopment towards tanks in the 30 ton class with relatively poor protection but with good mobility.

  3. Alternative S. An entirely new type of tank in the 30 ton class with low siluette, good protection and good mobility.

The studygroup requested a feasability trial of the realisationpossibility of the S-alternative regarding the possibility to aim the gun by swiveling the chassi with trackmovement and the frontal protection against HEAT rounds. In october 1957 a 9 ton assault gun (Ikv 103) was connected to a hydraulic system of a tractor to test the idea of the aiming system. The results were positive. The tests regarding frontal protection against HEAT rounds were conducted in 1958. The frontal possition of the engine and the frontal steelplate coupled to the amunition stowage at the lower rear proved that the Strv 103 would have the best protection in the world frontally. Until the Merkava (with its frontal engine), the M1 and Leopard II, the Strv 103 was the only tank that could resist hits from anti tank missiles frontally. The design of the side armor with its partly external fueltanks and after the renovation and mofication (REMO) with diesel jerrycans along the sides, also meant that the Strv 103 had the best protection against HEAT rounds. Tests showed that while a HEAT round would puncture and often ignite the diesel pouring out on the outside of the vehicle, the HEAT jet itself would start to dissipate in the diesel.

In 1958 the studygroup turned in their report with suggestions for technical and tactical specifications for new tank and recommended that the S-alternative should be further tried by trials in the 30 ton class. The defence decision in 1958 meant that the commander of the army decided to develop a new tank. The project S thus ordered Bofors to manufacture a number of testriggs. The aiming system and a fixed main gun was tested on a 30 ton Shermanchassi. The need for elevation and depression was tested on a Strv 74 (also developed by Sven Berge) chassi with a long gun barrel mounted on the chassi. A hydropneumatic suspension was tested on the chassi of another earlier swedish tank project, the KRV. On this rigg aiming and firing tests were conducted in 1959-1962

The KRV-rigg.

During 1958-1959 an investigation regarding engine alternatives was conducted. After inquireries and visits to USA, England and West-germany the information gathered showed that the best alternative would be a combination of dieselengine and gasturbine. Of the twelve available altenatives it was only the british Rolls Royce K60 and in combination with the american Boeing 502 gasturbine that fitted in the dimensions already decided upon. The advantages of the gasturbines lower weight and volume came at the price of higher fuelconsumption and inferior acceleration.

With the purchase of the Centurion Mk 10 in 1959 from Britain Sweden aquired permission to manufacture its 10,5 cm gun. This spared the project S to have to develop a new gun. The barrel on the Strv 103 became one meter longer. L/62 compared to the L/51. This meant a a higher muzzle velocity which in practise extended the effective range 500 meters for a given penetrention. The fire power was thus higher than in contemporary tanks. With modern APFSDS rounds the effective range has been even more increased. (Although the hydrodynamic penetrention procedure of these rounds mean that the length of the penetrator is more important than sheer speed and thus the Strv 103 advantage over other tanks has diminished.) The longer barrel also meant a less amount of dust thrown up when firing. This can mean that the Strv 103 will manage a higher rate of fire under dusty conditions. This was confirmed in tests at the armored combat school in 1977. In 1960 ten trial tanks were ordered, the so called 0-serie. They started to be delivered in 1963.

A 0-series tank with Pbv 302 and armored infantry.