The U.S. Navy is planning on constructing Pearl Harbor’s first covered dry dock and first new submarine repair facility at the Hawaii installation since World War II, Navy Times reports.

A notice to contractors by the Navy in May estimated construction costs would be between $2 billion and $4 billion. Although Pearl Harbor has four existing dry docks, a deeper facility is needed to accommodate large submarines. Security officials say that enclosing the dock would deter foreign adversaries from spying on the U.S. technology.

The modernization effort at Pearl Harbor falls under the Shipyard Infrastructure Optimization Program, a $21 billion effort over 20 years to improve four outdated Navy shipyards.

Navy officials say that a completion date cannot be determined at this time.

Photo by Petty Officer 1st Class Daniel Hinton