[dmurray]

Attack submarines are much smaller than missile subs. I don't understand exactly why this is and what the trade offs are here - manoeuvrability, cost? They seem to need approximately the same size crew of 100-150.

The closer comparison would be to the US Ohio-class missile sub, which is 3x the size of the LA class with the same complement.

https://en.m.wikipedia.org/wiki/Ohio-class_submarine

[masklinn]

> Attack submarines are much smaller than missile subs. I don't understand exactly why this is

SLBM are big, a Trident II is 13.6m long and 2.11m wide[0] and Ohios need to fit them straight up plus the hull, so we're talking 14m moulded depth or so (excluding the sail), and a pretty similar beam, at which point… you just have a big sub, because it can't exactly be a ball: you need to fit 12 Tridents in a row, plus the reactor, engine, crew compartments, passages for the crew to move around, torpedo tubes, and enough stores to last for literally months.

Attack subs can have vertically mounted cruise missiles but those are puny compared to an SLBM, a Tomahawk is 6.25m long with booster[1]: an Ohio-class carries 24 Tridents in SSBN configuration, if converted to SSGN it carries 154 tomahawks.

Los Angeles carries 37, Seawolf carries 50 (and on both this competes with torpedoes and anti-ship missiles, on an Ohio you get 24 tridents or 154 tomahawks plus a dozen torpedoes or anti-ship missiles).

[0] and Typhoon's SLBMs were even larger at 16.1m by 2.4

[1] and 0.5m wide

[goatinaboat]

SLBM are big, a Trident II is 13.6m long and 2.11m wide[0] and Ohios need to fit them straight up plus the hull, so we're talking 14m moulded depth or so (excluding the sail),

There are designs that use the sail, the North Koreans are using that configuration. They took old Romeo class and extended the sail back along the hull to fit 3 launch tubes. But the tubes extend so far down into the hull that they have had to remove batteries in order to do it. Which is a pretty severe compromise as what you absolutely want in such a sub is endurance.

Interestingly they have designated those missiles Pukkuksong, which translates as... Polaris!

[jbc1]

The Typhoon was also built to operate in the Arctic. The bigger it is the more ice it can punch through to fire missiles.

[dmurray]

I didn't consider that the missiles need to be stored vertically, but that makes a lot of sense, thanks.

[masklinn]

Technically they don't need to, but storing them vertically means you don't have to surface to launch: if you can make the missiles buoyant (at will, usually by pumping gas or vaporising a bunch of water when you want to launch them) they'll pop out the water like corks at which point the rocket engines fire and off it goes. This means your sub can stay safe and secure below the waves while launching.

[dmurray]

Why do you need them vertically stored for that scenario? Couldn't you make the front of the missile more buoyant than the rest, so once you pop it out of the sub it self-rights and likewise pops out of the water?

I imagine flipping from horizontal to vertical would put stresses on the rocket body, so there are engineering problems to solve, but still it's surprising that the only way to solve that problem has to been to build a launch platform 5 or 10 times bigger than is otherwise desirable.

[masklinn]

> Why do you need them vertically stored for that scenario? Couldn't you make the front of the missile more buoyant than the rest, so once you pop it out of the sub it self-rights and likewise pops out of the water?

That would make the entire thing more complicated with more chances of failure because now the SLBM wobbles around when it tries to right itself up (on a non-aerodynamic axis so more chance it'll move wrong), you need much bigger openings for the missiles, and your gain will be limited: remember, they're 2m wide so if you stack them by 4 you still need 9m for the missiles alone except now you also need to have 3 rows of missiles meaning you need a lot of extra horizontal space (in the current configuration the missile compartment of an Ohio is about 40m, it'd need to be 60+). It also makes the launch procedure take longer, as the missile can't accelerate as fast out of its casing: it doesn't just pop straight up like a cork anymore.

[jabl]

Also, reportedly Soviet ballistic missiles were/are less accurate than US ones, so they compensated by having a bigger bang, in turn needing a bigger missile to launch it.

Another solution would be to do what the North Korean missile subs, putting the missile tubes in the (lengthened) sail.

[masklinn]

> Another solution would be to do what the North Korean missile subs, putting the missile tubes in the (lengthened) sail.

The US used to have something like this in the Regulus, their intended launcher (the Grayback-class) essentially had hangars.

The great advantage of SLBMs is that the vertical mounting and a good enough launch sequence means you don't have to surface to launch: https://youtu.be/sUlXty69-Y8

[chiph]

You need a certain diameter of the pressure hull in order to accommodate the length of the missiles and their launch tubes. Also a factor - the range of the missile. Want a longer range? You'll need more fuel and the missile gets longer. Which means you need a bigger sub.

[brandmeyer]

> I don't understand exactly why this is and what the trade offs are here - manoeuvrability, cost?

Payload. One type carries a couple dozen medium-range ballistic missiles, and the other doesn't.

[dmurray]

The Ohio-class carries 24 60-ton Trident missiles, 1,440 tons of dead weight. That doesn't seem like enough on its own to justify the difference in displacement of 18,000 tons vs 6,000 on the Los Angeles-class. (I'm just getting these numbers from Wikipedia so may misunderstand something)

[chasd00]

"24 60-ton Trident missiles". wow, so let's say each has a MIRV with 5 W88 warheads at 500KT each. That's about 120 independently targetable warheads (each 6-7x more powerful than the Fatman nuclear weapon dropped on Nagasaki) per submarine. Wikipedia says they are on 14 Ohio class subs operated by the US. That's 1,680 total but let's say only 75% are operational at a time. So the US Trident II SLBM cocked-locked-ready-to-rock capability is around 1.3K 500KT warheads alone. That's... a lot.

[angry_octet]

More like half active, a quarter in port or in light maintenance, a quarter in deep maintenance. Realistically, two always on station from each fleet, sometimes four. Enough to maintain second strike deterrence even with enemy attack subs to contend with.

It also important to note that once an SSBN launches, there will likely be return fire from either land or sea based ballistic missiles that will boil the ocean for 50nm, incoming in 30-60 minutes. So tactically it is hard to launch just one nuke... It's full commitment or nothing. Just another cheery aspect of escalation dynamics.

[dragonwriter]

> So the US Trident II SLBM cocked-locked-ready-to-rock capability is around 1.3K 500KT warheads alone. That's... a lot.

Aside from overstating operational readiness, you also upped the W88 yield from it's actual 455KT and, while most sources do reported that 4-5 warheads per missile is typical, you assumed all in the fleet or W88s, while they seem to be a mix of W88 and 90KT W76.

So it's a lot less ready to go than you've estimated here.

But, OTOH, it's still a lot.

[dragonwriter]

> Attack submarines are much smaller than missile subs. I don't understand exactly why this is

Because a missile sub is, loosely, an attack sub with an ICBM base strapped to it. (Yes, technically SLBMs aren't ICBMs, but late Cold War SLBMs had ranges greater than the upper end for IRBMs, and so would be ICBMs if land based.)

> and what the trade offs are here - manoeuvrability, cost?

The boomer trades off maneuverability for the ability to destroy a moderate-size country with nuclear hellfire from thousands of miles away.