Matson Inc., Hawaii’s largest ocean cargo transportation company, will have not just two new ships, but four serving the state in the next few years.

The company announced Thursday that it has placed a $511 million order for two ships it expects to receive in 2019 and 2020 for its Hawaii service. The deal follows a $418 million order made in 2013 for two ships that started getting built last year and are due to begin service in 2018 and 2019.

Matson is making the upgrades in part to improve its efficiency and to avoid the need for costly upgrades on older ships that can’t continue operating after 2020 without improvements because of federal pollution control regulations.

The two newest ships will be able to carry the equivalent of 3,500 20-foot containers, or TEUs, plus up to 800 vehicles. These so-called roll-on/roll-off, or ro-ro, ships will replace older and smaller ships, including one ro-ro vessel that was built in 1973.

As has been a tradition at Matson, the new ships will be named the Lurline and Matsonia, inheriting those names from older ships that have been or will be retired. In Matson’s 134-year history, there have been five Lurlines and four Matsonias.

Other features of the ships just ordered include a more fuel-efficient hull design, double-hull fuel tanks, freshwater ballast systems and engines that will run on fuel oil but can be adapted to run on liquefied natural gas.

“This vessel order underscores Matson’s long-standing commitment to serve Hawaii with the largest, most reliable, efficient and environmentally friendly fleet for the long term,” Matt Cox, Matson president and CEO, said in a statement.

Matson expects a roughly 30 percent fuel savings per TEU as well as lower costs for crews, maintenance, repairs and dry-docking.

When the first two new ships go into service, Matson will be able to run 10 vessels instead of 11 in its Hawaii service. That’s because the newer ships have around twice as much capacity as Matson’s oldest ships. After the second pair of new ships is added, the number of vessels operating can be reduced to nine, Matson said.

The four new ships will allow Matson to retire seven older steam-powered vessels built in 1978 or earlier: the Matsonia, Kauai, Matson Navigator, Maui, Lihue, Matson Producer and Matson Consumer, of which the last four are reserve ships not in service.

Seven newer ships operated by Matson are diesel powered and were built between 1982 and 2006. Three of these will be put into reserve for use during an emergency or during scheduled dry-dock maintenance of the regular fleet, though Matson has not identified which ships will be put into reserve.

The average age of Matson’s fleet in 2020 when all four new ships are deployed will drop to 13 years from 27.

The two most recent ships will be built by General Dynamics NASSCO, a San Diego-based subsidiary of General Dynamics. The two ships under construction are being built by Aker Philadelphia Shipyard in Pennsylvania.

Building the ships in the United States adds considerably to the cost, but federal law known as the Jones Act requires that ships operating directly between U.S. ports be built in the country.

MATSON’S HAWAII FLEET