The United States next year is slated to begin reducing launch tubes on each of its Ohio-class ballistic missile submarines, a new independent report states.

The elimination of four operational launch tubes on each of the 14 submarines that make up the Navy's Ohio submarine fleet will be the first substantial reduction in U.S. strategic weapon delivery capability since the 2011 New START accord went into effect, according to Hans Kristensen, who co-authored an assessment on the current status of U.S. nuclear forces. The report was published in the January/February edition of the Bulletin of the Atomic Scientists.

Nearly three years after the New START pact with Russia entered into force, implementation of the treaty has "been going very slowly," Kristensen said in a brief Monday phone interview.

The treaty requires Russia and the United States by 2018 to each reduce their fielded stockpiles of strategic nuclear warheads to 1,550 and to cut their arsenals of long-range delivery vehicles down to 700 apiece, with an additional 100 systems allowed in reserve on each side.

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"The way that the U.S. military has approached implementation of the New START treaty so far has not done anything that has actually affected the actual number of nuclear [delivery vehicles] that are in the war plan," said Kristensen, who directs the Nuclear Information Project at the Federation of American Scientists.

Instead, the Pentagon has focused on reducing the nuclear-delivery capability of selected vehicles, such as heavy bombers, that have already been retired, he said.

The Defense Department has the latitude to pursue that approach because the treaty allows so many years -- seven, specifically -- before each side must carry out all mandated reductions, Kristensen said.

Once all of the Ohio-class submarines have had their launch tubes capped at 20 each -- a project that is to take place in the 2015-to-2016 time frame -- the United States will be able to deploy no more than 240 submarine-launched ballistic missiles at any time, according to the report written by Kristensen and Robert Norris, who is also with the Federation of American Scientists.

The submarine set to replace aging Ohio-class vessels -- dubbed "SSBN(X)" -- is expected to have only 16 missile tubes, which will reduce further the number of sea-launched ballistic missiles that the United States can deploy. The replacement fleet is also envisioned to be smaller -- only 12 submarines instead of the current 14. The Navy is not expected to begin building the first boat before 2021, and could field the vessel a decade later, according to the Bulletin report.