The Stridsvagn 103 (Strv 103), also known as the Alternative S and S-tank,[4] is a Swedish Cold War-era main battle tank, designed and manufactured in Sweden.

In the early 1950s, the Royal Swedish Army Materiel Administration's Ordnance Department began development of a new tank known as kranvagn, or KRV.

The new design emerged with a very low-profile hull with a tall and highly angled turret mounting a large-calibre main gun and autoloader system, reducing the crew to three.

"Alternative A" (for "Anglo-American") was to purchase a design from either the British or Americans of roughly 50 tons but mounting a more powerful gun than the Ordnance QF 20-pounder of the existing Centurions.

This featured a large (for the era) gun in the hull that was fixed in azimuth, and required the entire tank to turn to aim it.

[11] The resulting chassis was quite small, with only four road wheels, and the gun extended through the vehicle to the rear where the autoloader and ammunition was stored outside of the crew compartment.

The resulting 30 ton design offered the same level of armour as the heavy tanks, but was better protected overall due to the external ammunition and very low profile.

S would be the most expensive, but it was ultimately selected for the symbolic value of a domestic tank in a neutral country as well as the spin-off effects on Swedish industrial competence.

Because the gun was fixed in place, with no recoil movement, the autoloader was able to reach the very high rate of firing every three seconds.

The decision was made to add a third member, assigning them to operate the radios as well as having a second set of controls and vision systems to allow them to drive the tank in reverse at high speed.

John F Kennedy expressed an interest in the design, leading to a memo by Robert S McNamara noting: Their new tank has advantages over our M60 in its low silhouette, lighter weight and amphibious capability.

[citation needed] The radical solution was to eliminate the turret, which would also dispose of a vulnerable target area and make the tank much lighter.

Since the Strv 103 orients the entire tank to depress and elevate the barrel, in a hull down position it has very little apparent height and subsequent visual profile to the enemy.

[citation needed] Being familiar with both the French Char B1's precision transmission, the exceptional turning performance of the short tracked assault guns, and the combat performance of the German StuG and Jagdpanzer series inspired Berge's design to solve the aiming problem through the use of a fully automated transmission and suspension system, which precisely turned and tilted the tank under the gunner's control.

The rifled gun, a Bofors 105 mm L74 with a barrel length of 62 Calibers, was able to use the same ammunition as the British Royal Ordnance L7, and would be equipped with an autoloader allowing a rate of fire of one round every three seconds, also allowing the crew to be reduced to two; a gunner/driver and the commander (most designs of the era used a crew of four), with one person being able to handle all functions of the tank from the ordinary position due to duplicate controls.

This would of course only be used in emergencies, as the workload would be overwhelming, but apart from providing redundancy it also allowed the crew to shift tasks between them as situation required.

The concept went through practical tests, that quickly revealed that a two-man crew would not be self-sufficient when considering the many tasks not directly related to handling the tank: in particular, routine maintenance, bivouacking, track-changes and reloading in field.

This allowed the tank to be driven backwards at the same speed as forwards, keeping its frontal armour pointed at the enemy, while relieving the commander of routine radio duty.

A flotation screen could be erected around the upper hull in about 20 minutes, and the tracks would drive the tank at about 6 kilometres per hour (3.7 mph) in water.

The blade allowed it to do simple engineering tasks, like digging fire pits for the platoon, filling trenches for ease of passage and so forth.

Upon the introduction of the 103C model all tanks had a bulldozer blade fitted, both to speed up operations and for the increased protection of the lower hull.

[citation needed] With minor changes, the Alternativ S was adopted as the Stridsvagn 103 ("103" from being the third tank with a 10 cm calibre gun accepted into Swedish service).

The changes included a new gyro-stabilised commander's cupola armed with a 7.62 mm KSP 58 machine gun, and upgraded frontal armour.

A unique slat armor grid could be mounted at the front to help defeat high-explosive anti-tank (HEAT) rounds; however, it was kept secret for many years and was to be fitted only in the event of war.

In April to September 1968, two 103s were tested at the British armour school in Bovington, which reported that "the turretless concept of the "S"-tank holds considerable advantage over turreted tanks".

Over nine days of manoeuvres alongside the Chieftain tank, availability never fell under 90% and the final report stated, "It has not been possible to prove any disadvantage in the "S" inability to fire on the move.

[11] In comparison with the Centurion, the shorter track of the Strv 103 meant it performed worse on soft ground (mud and snow), and its trench taking and vertical obstacle capabilities were also significantly lower: where the Centurion climbed a 100 cm wall, the 103 was barely able to climb an 80 cm wall.