Plymouth P5 is a make of car available in L.A. Noire.
It is identifiable from the headlights, front apron and grille as a 1937 P4 model. It is incorrectly identified as a 1938 P5 model. It's possible that the 1938 export model was identical to the 1937 USA model, so the in-game identification would be correct for the UK.
It can be found in the case "Upon Reflection" in one of the parking lots (closest to 6th St.) west of the crime scene.
It can be found on the mission Canned Fish as the pursuit vehicle.