Many other countries have SLBMs. They're possibly the most reliable "second-strike" weapon. This was a particular concern for the UK as it's very close (relatively) to the USSR; in the event of a nuclear war the US would have had enough warning to scramble bombers / evacuate the president / etc. in a way that the UK wouldn't.
That's one part of the reason the UK doesn't have air-launched nuclear weapons. But really they fell out of favour ever since Gary Powers was shot down; ballistic missiles are inherently a lot harder to intercept than planes. I suspect the reason other countries still have them is mostly residual, and a reflection of the fact that those are the countries that still fly heavy strategic bombers. If you already have your B-52 (or Russian equivalent) fleet carrying heavy bombs and air-launched cruise missiles, it costs relatively little to maintain the capability to put nuclear warheads on those missiles. AFAIK the UK simply doesn't fly a heavy bomber any more - only the Tornado.
Land-based silos make sense for countries with large areas of empty, relatively unpopulated land, which the UK isn't. France doesn't have any either. I suspect India only uses land-based weapons because it can't maintain a sufficiently reliable submarine fleet.
Non-ballistic nuclear missiles still a purpose beyond the intertia of keeping them in service, they're the "stealth strike" option. A cruise missile is designed to hug the terrain, avoiding radar detection through proximity to ground clutter and its small radar profile which can be mistaken for an aircraft.
ICBMs are impossible to intercept once they're past the initial launch stage but they are very easy to detect which kicks off a retaliation. A cruise missile with "modern" stealth design would be an incredibly threatening weapon as you'd only need ~100 or so to cripple the retaliation capability of another nuclear power.
> A cruise missile with "modern" stealth design would be an incredibly threatening weapon as you'd only need ~100 or so to cripple the retaliation capability of another nuclear power.
You would? Such a thing wouldn't work against nations that maintain a constant submarine patrol, and perhaps not against land-based silos either (which were designed to withstand such attacks, no?) Heck, ISTR some of the Russian weapons were rail-mounted and designed to be hidden in mountain tunnels most of the time.
That's one part of the reason the UK doesn't have air-launched nuclear weapons. But really they fell out of favour ever since Gary Powers was shot down; ballistic missiles are inherently a lot harder to intercept than planes. I suspect the reason other countries still have them is mostly residual, and a reflection of the fact that those are the countries that still fly heavy strategic bombers. If you already have your B-52 (or Russian equivalent) fleet carrying heavy bombs and air-launched cruise missiles, it costs relatively little to maintain the capability to put nuclear warheads on those missiles. AFAIK the UK simply doesn't fly a heavy bomber any more - only the Tornado.
Land-based silos make sense for countries with large areas of empty, relatively unpopulated land, which the UK isn't. France doesn't have any either. I suspect India only uses land-based weapons because it can't maintain a sufficiently reliable submarine fleet.