Armament 107
The appearance of tubes above or below the gun on most self propelled howitzers are called recuperates. They help to reduce recoil and can be used to identify the difference btween the 2S1 and the 2S3. The 2S3 has two recuperates mounted side by side over the barrel where as the 2S1 has two but they are covered by a shield.
2S1
2S3
The muzzle break at the end of the gun can provide a clue as well.