When subtypes of one aircraft have different roles, they also have different function letters. For example, the fighter version (with a secondary attack) role of the Saab 337 Viggen is the JA 37; but the attack version (with a secondary fighter role) is the AJ 37.
A = Attack B = Bomb Fpl = Flygplan (aeroplane; used for multirole light aircraft) Hkp = Helikopter J = Jakt (fighter) S = Spaning (reconnaissance) SF = Spaning foto (photographic reconnaissance) SH = Spaning havsövervakning (maritime reconnaissance) Sk = Skol (trainer) T = Torped (torpedo bomber) (obsolete) Tp = Transport