 Complete the following phrase:  The 5-inch51 caliber gun was designed to engage destroyers, torpedo boats, and other surface targets. The 551 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 a href526quot3B3820caliber20gun538 caliber gunas in later battleships, and some of the World War I-era battleships were rearmed with dual purpose guns as well. Surplus 551 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-inch51 shore batteries were used with great effectiveness by the 1st Marine Defense Battalion during the 