[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.