The 5-inch/51 caliber gun was designed to engage destroyers, torpedo boats, and other surface targets. The 5"/51 gun entered service in 1911 as secondary armament on the s, which mounted 16. The guns served well through World War I, but increased awareness of the need for anti-aircraft protection (especially following the attack on Pearl Harbor) encouraged mounting of dual-purpose &lt;a href="5%26quot%3B/38%20caliber%20gun"&gt;5"/38 caliber gun&lt;/a&gt;s in later battleships, and some of the World War I-era battleships were rearmed with dual purpose guns as well. Surplus 5"/51 guns from scrapped or rearmed battleships were mounted in United States Coast Guard cutters, auxiliaries, small aircraft carriers, coast defense batteries, and Defensively Equipped Merchant Ships. A 1939 Table of Organization and Equipment shows Marine defense battalions were equipped with six of these guns each. 5-inch/51 shore batteries were used with great effectiveness by the 1st Marine Defense Battalion during the Battle of Wake Island in December 1941. These were replaced in the defense battalions by the 155 mm Long Tom gun by 1943. Six s were rearmed with "wet mount" 5-inch/51 guns during World War II, taken from "Barracuda"-class submarines or spares for that class.