Portsmouth Naval Shipyard should not be on the Base Realignment and Closure list. I do not say this because the yard is important to the economy of New Hampshire, though it is. And not because the yard has a proud record of on-time delivery, below cost, though it does. Nor because the yard is a fine homeport to three medium-endurance U.S. Coast Guard cutters, though that is quite true.

No, my reasons are much more important than that. It is a matter of national security.

The United States is a maritime nation, utterly dependent upon the sea for our way of life. Yet we are, without a fight, surrendering our seapower to other countries. We are losing our capacity to build and repair ships.

In 1955, America had 1,072 U.S. flag merchant ships. Today there are 93. In 1955, the U.S. flag fleet tonnage represented a quarter of the world’s merchant ships. Today it is two percent. Our merchant fleet — its building, repairing, and operating — has been outsourced to other countries.

Our citizenry owns an acute case of sea-blindness. We are the richest have-not country in the world. More than 90 percent of the world’s trade is by water. The cars we drive, the clothes we wear and the coffee we drink all come to us in ships.

The only ships of any size being built in the United States are for the Navy and Coast Guard. These service fleets also have similarly shrunk considerably since 1955. Oh, I know the argument that our own Navy is still bigger than the next 13 combined. However, that says more about the willingness of other countries to let America do all the heavy lifting when danger looms. And there is also the mistake of thinking — and the U.S. Navy can be guilty of this, too — that navies exist to fight other navies. No. Navies exist to keep the sea lines of communication open.

Some among us can remember when there were large naval shipyards in Boston and Brooklyn. These people may also remember when civilian shipyards in Quincy and Boston would regularly overhaul destroyers. Those days and those shipyards and skilled workers are gone. And the same elegy can apply to southeastern waters and the West Coast. Most of the yards are gone and the skilled hands are aging.

For that reason the United States should retain Portsmouth Naval Shipyard, a place where ships can still be built and overhauled. Such knowledge and skills are not the purchase of a day and are more easily kept than developed. And having them in abundance is just as much a matter of national security as a squadron of F-16s or a Navy SEAL team.

America desperately needs all of its shipyards, including Portsmouth.

Raymond J. Brown is a retired U.S. Coast Guard captain from Londonderry.