ICBM vs Submarine Launched Ballistic Missile Size

So I was thinking about ICBM vs SLBM the other day and I noticed something interesting. The Trident D5 missile is substantially larger than the Minuteman III (130,000 lbs for former, versus 80,000 lbs for later).

That was surprising to me because I think of the subs being able to get closer to their target, so I would expect them to be smaller. There ICBMs have to travel all the way from Wyoming or wherever.

Is it because the SLBM’s carry more reentry bodies?

Paging Strange on a Train!

If you want to page someone, try this way instead: @Stranger_On_A_Train. The leading at sign actually pages them. It also acts to verify the proper spelling of the username.

Thank you.

And I tried to correct a spelling error in my post, but it looks like I can’t edit posts. Is that correct?

I had no idea the Trident was larger than the Minuteman III and I’m interested in seeing a definitive answer. If I might venture a guess, perhaps because silos are orders of magnitude cheaper than submarines, it is not necessary to concentrate as much firepower at a single ICBM site. You want to load up a $3 billion sub with as many kilotons of destruction as it can carry per missile. For that $3 billion dollars, you can spread your warheads among a whole lot of silos and Minutemen, making it more difficult (and expensive) for an enemy to target them all.

The Minuteman 3 carries 3 warheads of 300 kt with a 13 000 km range.
The Trident D5 carries 8 (and up to 12) warheads of 100 to 475 kt at 11 300km.
So yes apparently the extra weight is for the multiple heads.

The point of ballistic missile subs isn’t to get closer to their targets, it’s to put the missiles out of harm’s way. That’s why they emphasize being hard to detect over, say, speed.

A submarine launched ballistic missile is still an intercontinental ballistic missile. They’re going to be made as large as they need to in order to get the intended throw weight and range, and they’re not conceding anything to the Air Force’s ICBM mission.

Down deep, each strategic missile service believes their own offering is fully sufficient and the money spent on their rival’s systems are a waste.

I would guess the additional weight and mass is all the protective stuff that an SLBM needs to survive being underwater for the time it takes them to float to the surface, then launch. Plus the stuff to propel them out of the tube to begin with. A highly specialized environment.

I know they are shot to the surface, but I do not think the weight delta is due to this (except maybe some case stiffening?).

The stuff that propels them out of the tube is part of the sub, so that is not part of their weight.

My guess would be the multiple warheads as well. Looking up the now retired Peacekeeper/MX ICBM which could also carry up to a dozen warheads, they weighed in at 193,460 lbs. There’s also a table on the Trident wiki entry showing the effect on range depending on the number of Mk5 Reentry Vehicles carried. The Mk5 RVs each only weigh 175kg, but it lists the range while carrying 3 as 13,482km dropping to 7,593km when carrying 8.

Am I the only one thinking “Death’s Head” right now?

Note that the original Minuteman dates from 1962 whereas the original Trident dates from 1979. A lot of progress on size and capability occurred in those 17 years.

The latest Minuteman III dates from 1970 whereas the latest Trident II / D5 dates from 1990. 20 years of progress in size & capability.

Range and payload are tradeoffs. Having more of one will reduce the other. The navy missiles carry more warheads and probably a bigger/heavier MIRV bus/delivery system. They also need less range since they’re going to be patrolling closer to their potential targets.

You also tend to want to spread out your land missiles since their location is known and you want them to be harder to attack by not concentrating them, so you can have more, lighter missiles. On the other hand, the navy has a limited amount of subs and wants to get as much firepower on them as possible - so you want concentrated firepower.

But there’s nothing inherent about this. You could make gargantuan land based missiles if you wanted to (and the Russians often did because their rocket accuracy sucked and they needed to chuck huge bombs to have a good chance of hitting a target). The minuteman is just an unusually light missile and ended up being the mainstay of US land based missiles due to cold war/post cold war nuclear politics.

Pfft, everyone knows that had 9 warheads and was launched from a tank!

I recently learned that the Trident III deploys an aerospike, a rod out the nose to break up airflow.

This enables hydraulic actuators attached to the first-stage nozzle. Soon after, the first-stage mo>tor ignites and burns for approximately 65 seconds until the fuel is expended; in addition, an aerospike atop the missile deploys shortly after first-stage ignition to shape airflow. When the first-stage motor ceases operation, the second-stage TVC subsystem ignites. The first-stage motor is then ejected by ordnance within the interstage casing.

Few things.

  1. As LSLGuy said, Trident is a generation newer than the Minuteman,

  2. The Minutemans contemporaries were not the Trident, they were the Polaris and the Poseidon. These weighed 16000 kg and 29000 kg versus the 36000 kg for the Minuteman. The contemporary of the Trident was the Peacekeeper missile (58,000 kg to 88,000 kg).
    I don’t know how much the Minuteman replacement, the LGM35 Sentinal will weigh.

  3. The submarines which carried the first generation USN SLBM were much smaller than the ones which carry the Trident D5 (5000 tonnes displacement versus 19000 tonnes).

The other SLBM that carries the Trident D5 is the British Vanguard class, which weighs in at a sleek 16,000 tonnes (but also only carries 16 missiles instead of the Ohio class’ 24).

The Soviet/Russian Akula (aka NATO reporting code “Typhoon”) was stupendous: 48,000 tonnes. But those are retired now. The current Russian Borei class is a good bit smaller, 24,000 t. Still bigger than the Ohio.

TL;DR behind the trivia dump: ballistic missile submarines are hella big so that they have ample capacity for lots of very large missiles.

The Typhoon carried the SS-N-20 “Sturgeon”.
That was an SLBM which was almost a 100,000 kg in mass. It’s dimensions were approximately those of the Peacekeeper ICBM.
The Vessel had to be so big to carry such a missile.
The Typhoon didn’t have a missile room. Rather the missile tubes were carried between the two large internal pressure hulls. (So the climatic scene in The Hunt for Red October couldn’t have happened.

Which ultimately demonstrates my thesis: an SLBM is a fully-fledged ICBM in every way, and the submarine to support and launch it can be as riduculously large as necessary, as long as the nation has the resources to engineer and manufacture it.

Agreed.

Back in the 1960s the largest rocket that could be fitted into a sub or into a silo were significantly different. Likewise the size & weight of warheads was such that there was a large trade-off space in yield vs range vs warheads per missile.

Advancing technology has largely eliminated those forced differences. And treaties have largely eliminated the MIRV/MARV dimension of the trade space. Which has led to a convergence in size, weight, and capability of ICBMs & SLBMs.

As the various treaties expire or fall into disuse / disrepair / disregard by one or more sides, and as the (nuclear) world becomes more multilateral, the MIRV / MARV trade-space will reopen. It’ll be interesting to watch and expensive to pay for.