[aeonik]

This doesn't make sense to me. I would assume the engines starting by themselves would introduce enough error to throw the entire system off. Let alone natural seismic events in the ground, plus wind.

I would guess you must solve the 3D problem at least to some degree.

[ethbr1]

I'm not a rocket scientist, but I think thrust is pretty constant at that scale. That's why they start, spool up, then release from cradle.

Vs something like a Polaris SLBM that has a much more variable guidance problem

It'd be curious to see how early ICBM and SLBM guidance systems differ.

[kens]

I haven't looked at submarine systems in detail, but my understanding is that the big problem is that an ICBM knows where it's starting, but the submarine travels. So submarines have super-accurate inertial navigation systems on board to determine their position.

[ethbr1]

I was thinking more for the sequence where it broaches the surface then lights its engine.

https://m.youtube.com/watch?v=h5KejRbD5s0&t=34s

That's a lot more dynamic of a launch orientation. Which way is it rotated? Is it inclined off vertical?