Do submarines have seat belts

No but they may be provided for the helmsmen who control the steering and ballast wheels as these things do (mooovvve) around under tension! They do have metallic strap hangers akin to subway cars for officers and crew to hold onto during tight maneuvers, etc. By the way many Naval vessels have Bannisters on the bulkheads-walls for similar reasons, in some cases even in the wheelhouses. in damage control situations, this can be a life-ladder indeed! glug glug hope you never have to use it, but there are bannisters on the walls in many ships.