Set it to "T", then attach a large format lens on an adapter with a bellows. Lock the mirror up. Fire the shutter on the body, then fire the lens shutter. Not dead silent, but close, at least until you're done with the exposure and want to advance the film. Alternatively, earplugs. On both you and your subject(s).
Although as George Lucas said, even in space where there is no air for the sound to carry, you need the sound for the movie effect.
... or all the space battles would be like a silent movie.
So as not to violate my sensibilities too much, I always imagine that I'm hearing the sounds from within the confines of the space vessels. It helps some.