[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!