The Ukrainian military has managed to integrate the donation of M-55S tanks from Slovenia into its operational forces. This contribution, made in April 2022, just two months after Russia expanded its offensive against Ukraine, included 28 M-55S tanks. This donation also brought a host of challenges that the Ukrainians had to overcome to best operate the Slovenian tanks.
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M-55S main battle tanks are now part of the newly established 5th Tank Brigade. (Picture source: Ukrainian MoD)
The integration process of these hybrid tanks, which merge the design of Soviet T-55 tanks from the 1950s with modern Israeli sighting systems and the British L7 105mm cannon, has been complex. Despite their superior armor and fire control systems compared to many Russian tanks, the unique combination of the M-55S posed challenges for its full utilization within the Ukrainian military framework.
Initially deployed with the 47th Mechanized Brigade, the M-55S tanks underwent intensive NATO-style training before being reassigned ahead of Ukraine's major counteroffensive in 2023. This move was strategic, aimed at strengthening the front line with the more heavily armored German Leopard 2A6 tanks, relegating the M-55S tanks to a reserve role within the 67th Mechanized Brigade.
The unfolding conflict saw these tanks holding positions around Kreminna in Eastern Ukraine, where they faced severe combat, leading to the loss of one M-55S to artillery fire. Following the stalemate of Ukraine's counteroffensive and subsequent Russian advances, the remaining M-55S tanks have been reassigned once more.
Recent developments indicate that the M-55S tanks are now part of the newly established 5th Tank Brigade. This unit, stationed in Kryvyi Rih in the south of Ukraine, has been actively preparing and stands as one of the few reserve brigades ready to be deployed. The formation of this brigade is particularly noteworthy due to its inclusion of Leopard 1A5 tanks, acquired through a collaboration between Denmark, the Netherlands, and Germany. These tanks, like the M-55S, are equipped with the L7 cannon, indicating a strategic amalgamation of firepower within the brigade.
The M-55S is a significantly upgraded version of the T-54/55 tank, which was originally put into service in 1947 and has become the most widely produced and used tank in the world. Over time, several nations have made modifications to the T-54/55 to extend the durability of this tank in their arsenals. Slovenia, for example, produced its modification, the M-55S, a variant little known until it donates to Ukraine in 2022 to assist that country in its conflict with Russia. This tank is distinguished by its improvements in terms of frontal armor, upgraded suspension, new tracks, increased engine power, and a cannon compatible with NATO ammunition.
The transformation from T-55 to M-55S began in the context of the Ten-Day War in 1991 when Slovenia declared its independence from Yugoslavia. After independence, Slovenia inherited all the JNA (Yugoslav People's Army) tanks left on its soil, including 54 M-84 and 30 T-55 tanks. Towards the end of the 1990s, Slovenia decided to modernize these tanks, with the T-55 being transformed into the M-55S with the help of the Israeli company Elbit Systems. This modernization included an improvement of the base armor, the addition of Israeli-designed explosive reactive armor, an update of firepower with the replacement of the original cannon with an Israeli version of the British Royal Ordnance L7 105mm cannon with a thermal sleeve, and improvements to the fire control and sighting systems.
In addition to improved armor and firepower, the M-55S also received an engine upgrade from 580 to 600 horsepower, as well as new suspensions and wheels to improve its cross-country mobility. Despite these substantial improvements, the M-55S, having a relatively quiet operational life, was placed in storage by Slovenia in 2016 and offered for sale, although there were no buyers.
However, in 2022, Slovenia donated 28 of its M-55S tanks to Ukraine, marking the introduction of the oldest tank formally introduced into the Russo-Ukrainian conflict, even surpassing Russia's use of the T-62. While tanks like the M-55S might seem outdated against modern anti-tank weapons, their role is not limited to direct combat against other tanks but also includes holding and defending positions. It's also important to note that the 105 mm cannon of the M-55S, among the best tank guns of the Cold War, remains competitive even today, illustrating the ongoing value of this weapon in the current context.
This third reassignment of the M-55S tanks is not merely a question of redistributing assets; it signifies the creation of a harmonized force capable of leveraging the commonality of the L7 cannon across different tank models. The 5th Tank Brigade exemplifies a new model of efficiency, with its combined battalions ready to offer a unified artillery front.
