Naval Base Saipan or Naval Advance Base Saipan or Naval Air Base Saipan was a United States Navy Naval base built during World War II to support Pacific Ocean theater of war and the many warships and troops fighting the war. The base was on the island of Saipan in the Northern Mariana Islands. The base was part of the Pacific island hopping campaign. The base construction started after the Battle of Saipan ended on July 9, 1944. US Naval Advance Base Saipan was constructed by the Seabees Naval Mobile Construction Battalions. The base was under the Commander Naval Forces Marianas. Saipan is 12 miles (19 km) long and 5 miles (8.0 km) wide. About 70% of the island was sugarcane cultivation at the start of the base construction. At the start of the Battle of Saipan, the island's population had about 30,000 Japanese troops and about 20,000 Japanese civilians. The city of Garapan was the administrative center for the Saipan governmental district.

US Naval Advance Bases were built globally by the United States Navy during World War II to support and project U.S. naval operations worldwide. A few were built on Allied soil, but most were captured enemy facilities or completely new. Advance bases provided the fleet with support to keep ships tactically available with repair and supply depots of facilities, rather than return them to the continental United States. Before Japan declared war on the United States the U.S. Navy had a single fleet-sized advanced base in the Territory of Hawaii at Naval Station Pearl Harbor. During the war the U.S. Navy Seabees built over 400 advance bases categorized by size. Naval bases were either Lions or Cubs while airfields were either Oaks or Acorns. Lions and Oaks were major facilities while Cubs and Acorns were minor. PT Boats typically would get a Cub and airfields with single runways were Acorns. The larger bases could provide refueling and overhaul; loading of troopship and cargo ships; and preparing amphibious assault ships. Some became major repair depots. The Seabees developed auxiliary floating drydocks were able to repair battle damage and do regular maintenance in the field saving ships trans-pacific trips for repair. A few bases also were developed to be R and R for all U.S. personnel. Most Advance Bases were built by the US Navy's Seabees in Naval Construction Battalions (CBs). At the start of the war civilian contractors were employed in construction. The Seabees in World War II built most of the airfields used by the United States Army Air Forces and United States Marine Corps, as they had the ships and cranes needed to transport the vast amount of equipment needed at the advance bases. The US Army and United States Coast Guard also operated out of many of these facilities. Seabees could build new or repair damaged runways, and with advancements in heavy bomber technology lengthen runways as needed. A few Naval Advance Bases were built for the Korean War and Vietnam War.