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The Vickers machine gun was developed on the basis of the earlier Maxim gun. The design prouded itself with great efficiency as well as almost a hundred percent reliability. These technically perfect Vickers guns were produced in really great numbers both for the army (these were water-cooled) and for the air force, where they were air-cooled. The British army had the Vickers in use well until the end of the 1960s, and in other countries' armies, the weapon served even much longer.
And as the Vickers machine gun remained in production for a long period, no wonder that the many production batches differed in various more or less important aspects. Now we have for you the WW1 variety of the Vickers. The later that saw usage in WW2 is under development.