Title kinda says it all, doesn't it?
We attached some scratch-built nose cone dowels to some Quest MicroMaxx engines and gave them a paint job to ward off seawater soaking through, then glued igniters in place with Elmers Wood Glue to further prevent seawater intrusion. Custom-built launch system on the submarine (also scratch-built) was a servo-activated relay that directed current from the sub's main batteries to the igniter when a switch on the transmitter was pressed.
Launch tube was a disused piece of antenna from an old transmitter; it free flooded when sub was underway, so rockets couldn't spend long in the tube before firing (several swelled and didn't emerge from the tube properly).
Rockets didn't fly straight and true, tumbling lots without fins, but they got quite a lot of altitude. Not to worry; no one was around our deserted firing area, and those of us on-site to shoot this video wore safety goggles. Still a "don't-try-this-at-home" situation, but we liked the results.
Hope you guys and gals enjoy!