It used parts of the Tomahawk system, the precision bombing was largely covered. Drones are supposed to be cheap. Billion dollar delivery platforms don't really align with that. This is the US Navy trying to keep a weapon system designed for the cold war. An attack submarine that isn't stalking boomers is a hole in the water into which money is poured.

Why are drones supposed to be cheap?

It's one of their main competitive advantages. If a drone launch starts costing millions of dollars, the benefit it has over a traditional aircraft fly-over starts to diminish.

I don't see traditional aircraft taking off from a submerged submarine any time soon. That would seem to be an alternative advantage to offset the cost.

actually, the Japanese already invented that in WWII - http://www.nbcnews.com/science/sunken-japanese-wwii-submarin...

Not true. You forgot the submerged part.

getting a live camera + weapons near a spot where a submarine is already positioned is probably a whole lot cheaper than the alternatives.

alternatives: satellite, long range bomber, surface fleet, seal squad...

That only applies to this iteration. I don't see any reason why submerged drone launches couldn't be made cheaper.

Doubtful. The exact submarine used for this test launched was used in combat as recently as 2 years ago (Libya). Precision bombing from a submarine has been a solved problem since the late 80s, if not longer.