As a teenager, a friend and I built an underwater rocket, with the idea that a solid model rocket engine would burn when submerged, provided we could get it lit. We started with an Estes model rocket (https://estesrockets.com/products/mosquito IIRC), inserted the engine and igniter, and sealed the entire exhaust end of the engine with hot glue, as well as around the seams elsewhere. We installed a standard launch pad in a big trash bin filled with water (our original idea of swimming into a lake was quickly scrapped) and wired everything up.
It worked. The rocket actually launched from underwater! But by the time it reached the surface, the drag of the water had ripped two of the fins off, so the in-air portion was pretty wild. We even caught the whole thing on 8mm film (this was in the early 90s).
It worked. The rocket actually launched from underwater! But by the time it reached the surface, the drag of the water had ripped two of the fins off, so the in-air portion was pretty wild. We even caught the whole thing on 8mm film (this was in the early 90s).