Why aren't turbo fan/jet engines used as boosters?

[DerekL1963]

5 hours ago, wumpus said:

I'm fairly surprised this was never developed for sub-launch.  Presumably the Navy was confident in subs to hide sufficiently close to their targets and that the range was "good enough".

SSBN launch tubes and eject systems aren't nearly as sensitive to weight as they are to volume, and the ducting takes up a lot of volume.   You also add considerable mechanical complexity.  You'll need a base fairing to prevent eject gas from simply 'blowing by' the missile via the ducts.   You can't eject the base fairing (which will have to be fairly hefty) too early lest you potentially foul the hatch, which means to avoid serious drag and having to lift the weight of water in the ducts you'll need an upper fairing as well.  That means a lot of heavy debris created at ignition, which could pose a danger to subsequent missiles.  (The existing closures (at least in US practice) are essentially just lightweight bits of fiberglass and some styrofoam, they don't pose a hazard.)
 

4 hours ago, sevenperforce said:

Nuclear stealth subs can camp out just off the coast, surface and fire nukes, and sink again in a matter of minutes. The target gets no warning whatsoever because the dV and flight time is so low.

Pretty much everyone had gotten rid of surfaced launched strategic systems by the early-mid 60's.    And the history of SLBM's is a history of increasing range...  This reduces transit time to where they can hit targets, and by giving them a larger area of ocean to hide in makes the other side's ASW problem significantly harder.

[DDE]

16 hours ago, DerekL1963 said:

And the history of SLBM's is a history of increasing range...  This reduces transit time to where they can hit targets, and by giving them a larger area of ocean to hide in makes the other side's ASW problem significantly harder.

Yep. Modern SLBMs are basically sub-launched ICBMs. Early boomers had to camp in the enemy’s ASW grid right off their coast, whereas modern SSBNs can launch without leaving their home ports.

[wumpus]

27 minutes ago, DDE said:

Yep. Modern SLBMs are basically sub-launched ICBMs. Early boomers had to camp in the enemy’s ASW grid right off their coast, whereas modern SSBNs can launch without leaving their home ports.

This is why I was surprised that air-augmentation isn't/wasn't bothered with.  But since subs are going to be nearly neutrally buoyant but space constrained, I can see why it didn't happen.