 The gun entered service around 1900 with the s, and was also fitted to s. By World War II these guns were found only on a few Coast Guard cutters and Defensively Equipped Merchant Ships.Low-angle 3″/50 caliber guns (Marks 3, 5, 6, and 19) were originally mounted on ships built from the early 1900s through the early 1920s and were carried by submarines, auxiliaries, and merchant ships during the Second World War.These guns fired the same per second ammunition used by the following dual-purpose Marks, but with range limited by the maximum elevation of the mounting.