The term "138 mm artillery" generally refers to a type of artillery piece that fires projectiles with a diameter of 138 millimeters. However, it is important to note that this specific caliber is not as commonly recognized in modern military artillery as others like 105 mm, 155 mm, or 203 mm. One example of artillery in this caliber is the Soviet D-30 howitzer, which is a 122 mm artillery piece (though slightly different).
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