A timpani.

A timpani (orchestral kettle drum). Bonham used it instead of his kick drum for the main riff, playing it with mallets. That deep, rolling, almost ominous sound is all timpani — not a standard drum kit.

He also hit a gong during the intro, but the timpani is the unusual one. It’s an orchestral instrument, not typical for a rock drummer in 1975. Bonham tuned it low and used it like a kick drum on steroids. The sustain and pitch bend are what make “Kashmir” hit different.

If you’re covering the song and trying to replicate it, a timpani is the sound. Or a deep floor tom with a loose head cranked low and some reverb. But it won’t be the same.

Bonham turned an orchestra instrument into a rock legend.