Notice the anti-drone cage, and the remote controlled machine gun on the rear of the command post.

“The improved KOT1 V2 command post armored vehicle receives orders from the observation post, processes them and, in a split second, forwards them to the self-propelled howitzer, which, in a short time, computes firing data and is ready for all fire missions.”-Sergeant Major Mladen Miletić, Command Sergeant Major of the 23rd Self-Propelled Howitzer Artillery Battalion

Externally the ‘M21’ Gvozdika looks like any other Gvozdika.

Serbia spent the past few years upgrading their 2S1 self-propelled 122 millimeter (122mm) artillery system with the latest digital targeting and communications electronics.

U.S. Army vehicle I-D training image from the Cold War.

During the Cold War, NATO referred to the 2S1 as the ‘M-1974 SAU-122’.  The ‘M-1974’ refers to when NATO observers first noticed the SPG (Self-Propelled Gun), during a July 1974 parade in Warsaw, Poland. The SAU-122 refers to the diameter of the gun bore.

Side note; both NATO and former East Bloc countries call the 122mm gun a ‘howitzer’.  Technically this is incorrect as howitzer refers to short tubed, easily transportable by infantry, artillery guns.  Guns that had barrels which were much shorter than that of the old Soviet 122mm.

During the Cold War, NATO referred to the KOT1 V2 command post as the ‘M-1976’ command post, or as the MTLB-u.  Both the 2S1 and the command post are based on the MTLB chassis.

Serbian Defense Ministry video:

This has video of Serb 2S1s launching rounds: Serbian 2S1 Gvozdika