The submarine USS Hawai'i and destroyer USS Paul Hamilton left Pearl Harbor dry docks last week as the shipyard completed a combined $22.5 million in repairs and maintenance on the two ships, the Navy said.

The Paul Hamilton received $20 million in hull preservation, shafting and valve work, the Navy said. The shipyard work is set to finish its work on schedule on May 21, said Capt. Lynn Hampton, head of the surface ship maintenance department at the shipyard.

The attack submarine Hawai'i is undergoing $2.5 mil-lion in routine maintenance and inspection and was dry-docked on March 30. The Hawai'i, the first Virginia-class submarine to be based at Pearl Harbor, was commissioned in May 2007 and arrived in its namesake state last July.

According to the Navy, the shipyard will perform its first "extended" dry-docking of a Virginia-class submarine in the summer of 2012.

"The USS Hawai'i docking and undocking have great significance for the shipyard," shipyard commander Rear Adm. (Select) Greg Thomas said. "Our future depends, to a large extent, on Virginia-class submarines. By successfully executing these complex evolutions on Hawai'i, we are demonstrating our ability to support the Navy's next generation of submarines."

About 90 percent of the shipyard's work is on submarines.

The Navy said Virginia-class submarines pose unique challenges that make dry-docking the 377-foot vessels more complicated than their Los Angeles-class predecessors.

Pearl Harbor has two Virginia-class submarines, the Hawai'i and Texas, with more due to arrive here. There are also 15 Los Angeles-class attack submarines based in Hawai'i.

The shipyard is the largest industrial employer in the state, with a combined civilian and military workforce of more than 4,800 and an operating budget of $687 million.