Difference between Westland Wyvern S-2 And S-4

[Seahawk]

Not sure whether  @Beefy is still on his ATDU trip but have just come across an nice large underside view of Brigard TF.1 RH747 on p.24-5 of Planes 10 (Nov/Dec 1983).  The caption says that, "instead of seeing front-line service, [it] was used for test purposes by the ATDU", which is not the same as saying the photo is of her during her ATDU service: could be pre-delivery.  Anyway, she's in 2-tone camouflage (DSG uppers/Sky undersides?) with C Type roundels and Black underwing serials.  Rocket stubs under the wings and, I think, a torpedo rack under the fuselage. 

[Beefy]

Thanks for that information, i shall see if i can find a copy for reference. Appreciate the help .