The M-55S is Slovenia's modernized T-55 main battle tank, rebuilt by ST Ravne with a 105 mm gun, explosive reactive armor, fire-control upgrades, laser-warning equipment, and NATO-compatible ammunition. During the 2014 Russia-Ukraine War, Slovenia committed 28 of the scarce upgraded tanks to Ukraine through a ring exchange with Germany, turning a reserve Cold War chassis into a Western-supported Ukrainian fire-support vehicle.
Slovenia agreed in September 2022 to transfer 28 M-55S tanks to Ukraine through a German-backed ring exchange; Ukrainian forces later operated the upgraded T-55 variant for tank fire-support tasks, with subsequent reporting and loss documentation showing the small fleet still in wartime service.
Role detailsM-55S designations refer to Slovenia's T-55 modernization family rather than a newly built tank line.
| Variant | Configuration | Designation notes |
|---|---|---|
| M-55 USP | Driver-training derivative | The Slovenian Armed Forces list the M-55 USP as a driver-training vehicle associated with the M-55S armored-units page. Sources: ST RAVNE M-55 S Main Battle Tank |
The M-55S page is best read alongside the wider T-54/T-55 family because Slovenia modernized existing T-55 hulls rather than fielding a new tank design.
| Compatible item | Item type | Compatibility evidence |
|---|---|---|
 | Base tank family | The Slovenian Armed Forces identify the M-55S as an upgrade of the T-55; secondary armor references describe the Slovenian work as a T-55 modernization built around a new 105 mm armament and updated survivability equipment. Sources: ST RAVNE M-55 S Main Battle Tank, T-55 in Slovenian Service and M-55S |
Secondary armor references describe the M-55S conversion program as complete by 1999 after ST Ravne rebuilt Slovenian T-55 tanks with a 105 mm gun, protection, and fire-control upgrades.
Sources: T-55 in Slovenian Service and M-55S
The Slovenian government announced that 28 M-55S tanks would be provided to Ukraine through a ring exchange with Germany.
Sources: Prime Minister Robert Golob in a telephone conversation with German Chancellor Olaf Scholz about current European affairs
Ukrinform reported that Ukraine had received the 28 M-55S tanks from Slovenia after the September ring-exchange announcement.
Sources: Ukraine receives 28 M-55S tanks from Slovenia
Defense Express reported continued Ukrainian use of the rare Slovenian M-55S fleet, including additional field protection on surviving vehicles.
Sources: Ukraine Continues to Operate Rare Slovenian M-55S Tanks
The M-55S reflects two adaptation cycles: Slovenia first rebuilt T-55 hulls for NATO-compatible service, then Ukraine received most of the small fleet as emergency armored fire support.
| Context | Documented detail | Source |
|---|---|---|
| Modernization package | The official equipment page lists a 105 mm gun, explosive reactive armor, fire-protection and CBRN systems, laser-radiation detection, and four-person crew. | ST RAVNE M-55 S Main Battle Tank |
| Family conversion | Armor references describe the M-55S as a Slovenian T-55 modernization rather than a newly built tank, with NATO ammunition compatibility as a key feature. | T-55 in Slovenian Service and M-55S |
| Ukraine transfer | Slovenia announced 28 M-55S tanks for Ukraine through a German-backed ring exchange, and Ukrainian state media later reported the tanks received. | Prime Minister Robert Golob in a telephone conversation with German Chancellor Olaf Scholz about current European affairs; Ukraine receives 28 M-55S tanks from Slovenia |
| Field service | Specialist reporting and loss tracking both place M-55S tanks in Ukrainian wartime service after delivery, including later field protection on surviving vehicles. | Ukraine Continues to Operate Rare Slovenian M-55S Tanks; Attack On Europe: Documenting Ukrainian Equipment Losses During The Russian Invasion Of Ukraine |
