Mr Cameron visited HMS Victorious, one of the Royal Navy's Vanguard-class submarines, which is returning from its 100th patrol.

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Mr Cameron had earlier visited HMS Victorious, one of the Royal Navy's four Vanguard-class submarines which keep Trident nuclear missiles continuously at sea, which is returning from its 100th patrol.

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It argues that the life of Vanguard-class boats can be stretched at most to 30 years, not to 44 years as the service of America's equivalent Ohio-class boats can be.

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One is to offer a new share class as Vanguard is doing with its giant Vanguard 500 Index fund ( VFINX).

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The multi-share class structure gives Vanguard fund managers flexibility in how they manage their funds.

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The four Trident submarines are the V-class ones, Vanguard, Victorious, Vigilant and Vengeance.

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If you invest in single asset class index funds like the Vanguard Total US Stock Market index or the Spartan International Index at Fidelity, you can easily compare the performance of your individual holdings to the market index they track.

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More than two dozen such funds have a share class that charges at least 10 times as much as Vanguard Group does.

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Consider the Vanguard Total Bond Market Fund, which has both a mutual fund share class (VBMFX) and an ETF share class ( BND).

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