The Obama administration has funded a replacement for the Trident missile submarine in 2029.
It said it had no plans to review the future of the Trident missile programme ahead of next year's referendum.
The Trident missile system, Britain's nuclear deterrent, is carried by submarines based at the Faslane naval base on the Clyde, near Helensburgh.
He transformed the tiny maker of bathroom scales into a global producer of sophisticated sensors that, among other things, help guide the Trident missile.
Mr Cameron's schedule included a visit to a Trident nuclear missile submarine based on the Clyde.
In March this year, he joined 94 other Labour rebels to vote against renewing the ageing Trident nuclear missile system.
This examines what would happen if an independent Scotland insisted on the immediate removal of the Trident nuclear missile submarines from their base on the Clyde.
But the number of submarines will be reduced as will the number of missiles per submarine, and a replacement for the Trident II missile is not scheduled until 2042.
However, its baseline version of the interceptor is already quite capable, which is why the Navy will conduct a test this spring to see how it fares against a Trident ballistic missile flying a longer, faster trajectory than the service currently is postured to counter.
It delayed development of a new nuclear bomber and a successor to Trident ballistic-missile submarines.
Each U.S. SSBN is capable of carrying 24 Trident missiles with up to eight warheads per missile.
The Atomic Weapons Establishment (AWE) in Aldermaston, Berkshire, provides the warheads for Trident, the UK's submarine-launched missile system.
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