How many ballistic missile submarines does the U.S. really need?

The Navy’s formidable fleet of nuclear-armed submarines is approaching the end of its lifespan, and there’s growing debate over how many are needed and how to pay for them. Jamie McIntyre, national security correspondent for Al Jazeera America on special assignment for the NewsHour, got a rare behind-the-scenes look at one of the most powerful weapons ever built.

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