The head of U.S. Strategic Command warned early this week of the “precipitous risk” in the next decade as the Ohio-class ballistic missile submarines reach retirement and are no longer able to go underwater.

“Each submarine is built to go down, under pressure, a certain number of times. Once you reach the end of life, it can’t go down anymore,” Gen. John Hyten said Tuesday before the Senate Armed Services Committee. “A submarine at the top of the water is not an effective deterrent.”

Hyten said he could not publicly specify when the Ohio-class boats would reach that point but said it will start toward the end of the next decade. Starting in 2027, the Ohio-class boats will be retired at a rate of one per year. It’s not possible to further extend their lifespan, according to Hyten.

The remarks were part of a larger argument he made about the need to modernize the U.S.’s nuclear arsenal and to keep the $100 billion program to replace the Ohio-class boats on schedule.

The U.S. will need to spend 6 percent of its defense budget to modernize its nuclear weapons, as opposed to the 2.5 percent it spends now, according to Hyten. The defense budget, as a whole, makes up more than 50 percent of U.S. discretionary spending.

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