Draft:T-55S1

The T-55S1 or M-55S1 is the main battle tank of the Slovenian army. The first cases were received in late 1997.

History
A few years ago, Slovenia started a program to upgrade its old 100mm armed T-55 s to a new standard known locally as the M-55S1. Some systems were designed and manufactured in Slovenia, especially in the field of optics, while other parts are supplied by foreign countries, including Israel.

Development
A few years after gaining independence, Slovenia began a program to upgrade its old 100mm armed T-55s to a new standard known locally as the M-55S1.

This upgrade is being carried out in Slovenia and the first modernized M-55S1s were returned to their units in late 1997 or early 1998.

While some subsystems were designed and manufactured in Slovenia, especially in the field of optics, other parts were supplied from abroad, including from Israel and France.

The exact number of T-55 MBTs that were upgraded to the new M-55S1 configuration is 55.

Technical review
The design of the upgraded M-55S1 is almost identical to the T-55

The upgrade carried out in Slovenia covers three main areas of the vehicle: armor, mobility and firepower.

The standard 100 mm D-10T gun was replaced by a 105 mm Royal Ordnance L7 tank gun, which can fire a wide variety of ammunition types, including High Explosive Anti-Tan k - Tracer (HEAT-T), a armour piercing fin stabilased discarding sabot (APFSDS-T) and High Explosive Squash Head - Tracer (HESH-T).

The 105 mm L7 gun fires with an electronic system, as does the 7.62 mm machine gun, which is mounted flush with the main armament. Some models also have a 12.7 mm machine gun on the roof.

The 105 mm diameter barrel was fitted with a three-piece thermal sleeve, which was said to reduce barrel recoil by more than 70 percent, helping to increase the weapon's accuracy.

A new computerized fire control system was installed in the M-55S1, which is claimed to allow it to attack stationary and moving targets with a high probability of hitting the first round while the tank itself is stationary or moving.

The firing system has three modes of operation, automatic, semi-automatic and manual. In manual mode, the crew must manually insert the type of ammunition to be used.

The gunner is equipped with a Slovenian Fontana SGS-55 two-axis stabilized day/night image sight with a laser rangefinder that feeds information to the fire control computer. A thermal version of this system is also available on some tanks.

The vehicle is equipped with the Slovenian COMTOS-55 for the commander, which allows him to use the main cannon instead of the gunner. At the same time, it enables distance determination, target selection and firing with the main gun/coaxial machine gun. This is installed below the existing TPN-10 scope, which with the image of the target coming from the shooter's view, is maintained by means of a charging device.

The Fontana CODRIS combined day/night periscope is available to the driver, which enables day (field of view 80°) or night (field of view 78°) driving simply by pressing a switch.

The standard T-55 has a turret and hull made of welded and cast steel armor, but for added battlefield survivability, the upgraded M-55S1 was equipped with Explosive Reactive Armor (ERA) on the turret bow, lower and upper hull panels, and on the sides.

This armor is said to be Israel's latest Super Blazer system, which provides a high level of protection against high-explosive anti-tank (HEAT) attack, but cannot be activated by small arms fire.

The upper part of the suspension is protected by a five-part rubber lining that provides two functions. The first is to help reduce dust, and the second is to activate the explosive warheads, in the shells, before they hit the vehicle's main armor.

For improved mobility, the vehicle's suspension was changed and now each side consists of five wheels with rubber wheels, a drive gear at the rear, a guide at the front and four return rollers. The new 580 mm width was equipped with replaceable rubber pads, and a hydraulic steering system was installed for the driver.

The standard T-55 was equipped with a V-12 water-cooled diesel engine producing 580 horsepower, but this one was replaced in Slovenia with a 600 horsepower diesel engine. It is also possible to install a new generator, which includes a MAN diesel engine with 850 horses. With a combat weight of 40 tons, this generator would provide a good power-to-weight ratio of just over 21 HP/ton.

The upgraded M-55S1 not only relies on its improved armor to survive on the battlefield, but is also equipped with the Fontana LIRD (Laser IR Radiation Detector and Warning) system. It consists of a main detector unit mounted on the roof, an indicator unit and a wiring harness. This allows the crew to take action such as moving to a new position or activating onboard devices such as smoke grenades.

On either side of the turret is a group of six IS-6 CL-3030 IS-6 Instant Self-Defense Systems for combat vehicles - which have been installed on Israeli armored vehicles for many years. This launches shells at a distance of 40 m and sets up a 60 m wide smoke screen that lasts for about two minutes, depending on the wind. Also, the tank can set up a smoke screen by injecting diesel fuel into the exhaust port on the left side of the hull.

Each engine and crew compartment is equipped with a fire extinguishing system. Each of these systems comprises optical detectors, cylinders filled with Halon 1301 gas, and a control device that can be operated automatically or manually. The M-55S1 features a completely new communications system that includes two new antennas, new radios, a VIC intercom system and an external telephone. The telephone is mounted on the rear of the vehicle on the right side and allows the accompanying infantry to talk to the tank crew.

Usage

 * Slovenia

Slovenia currently has approximately 27 of these vehicles in use, which are in reserve. At least one is in the Pivka Military History Park.


 * Ukraine

In 2022, Slovenia sent 28 tanks to the Ukrainian Army. In the fall of the same year, a video of the alleged destruction of an M-55S tank circulated on social networks, which was said to be the first example of the destruction of this type of tank.

In the Kremina area, the tank was hit by a 152 caliber laser-guided projectile of the Krasnopol system. In the middle of July 2023, however, a video of the same tank appeared, still defying direct attacks. The projectile that hit it did not penetrate the armor, but damaged the visors on the tank.

First ever M-55S1 tank was destroyed on 22nd of July in 2023 in Krimena region.

Out of all 55, only 1 is destroyed and 1 is damaged (according to statistics, only the Leopard 1A5 with 1 damage surpasses it in the Ukrainian war at the moment)