In 1917, the Twelfth Regiment (Public Works) was organized at Naval Training Station Great Lakes. When the US entered World War I in April 1917, the Navy had an immediate requirement to expand the Great Lakes Station in order to house, process, and train 20,000 naval recruits, this number would rise to 50,000 by the end of the year. Lieutenant Malachi Elliott, a graduate of the US Naval Academy, was appointed Public Works Officer at Great Lakes on 18 June 1917, at which time about 500 enlisted men had been assigned to the Public Works Department. Seeing that the department would need to expand with skilled craftsmen, architects, draftsmen, designers, and other professional and technical people, he began to screen incoming recruits with these skills. Finding many, but not enough, he expanded to recruiting civilians outside of the installation, getting many men willing to join the Navy as petty officers, with the understanding that qualified men could later apply for commissions. This allowed the Public Works Department to grow to nearly 600 men by July 1917. They were organized into the Twelfth Regiment (Public Works), which was essentially the Public Works Department because staff officers could not exercise military command. Lieutenant William C. Davis was appointed commanding officer of the regiment, he exercised military control, but the Public Works Officers exercised technical control. In October 1917, the regiment began building Camp Paul Jones at San Diego. With its completion, on 30 December 1917, the regiment became "fully operational" with 1,500 men organized into three battalions. By April 1918, the regiment consisted of 2,400 in five battalions. Men were withdrawn for assignments in the US and abroad. In spring of 1918, 100 men were given special mechanics and ordnance training before being sent to St. Nazaire, France, to assemble 14"/50 caliber railway gun. Later they would join the gun crews and perform combat duties along the railway lines in proximity to the Empire of Germany lines. The Twelfth Regiment reached its peak strength 5 November 1918; 55 officers and 6,211 enlisted men formed into 11 battalions. However, with the end of the war on Armistice of 11 November 1918, the regiment gradually faded away by the end of 1918.. How many months did it take to build Camp Paul Jones at San Diego?