NASA's Gemini missions launched on Titan II missiles, notable for a very strange sound at the moment before launch.

Even rockets need a little help getting off the ground. Start cartridges get the fuel and oxidizer flowing into the combustion chamber so the real fun could begin. In the case of the Titan II, that start motor made an oddly distinctive booping sound.

For a little more on start cartridges and the GeminiTitan rockets, check out the latest blog post over on Vintage Space: http://www.popsci.com/whytitanrocke...
Want more Vintage Space? Subscribe to the blog, find me on Facebook, Google+, Instagram, and Twitter as @astVintageSpace.