Wheelhouse

“Wheelhouses,” so sayeth Wiktionary, “are the small enclosed parts of a bridge which historically held the ship’s steering wheel”.

By extension of stone dead metaphor, one’s wheelhouse is one’s interest, competence or preference — ones bag, baby—articulated in a way that only an American would not respond to with a roundhouse slap upside the head.

Known in sailing circles as a cockpit, which is a much better name for the place where you would find the sort of gent who uses the expression “wheelhouse”.