The mysterious SLC dial was originally made in the late 1950s as a stealth version of the usual dial. Interviews with former navy frogmen revealed that Panerai dials were extremely luminous and especially during night operations could give away the location of the divers and thus compromise the whole mission. In order to avoid being discovered from surface sentinels, the divers had to cover their watches and instruments with cloth or mud.
Panerai 6152/1 with S.L.C. dial (c) Photo credit Jose Pereztroika
Panerai 2533 with S.L.C. dial (c) Photo credit John Goldberger
Special credit for Jose Pereztroika. Vintage Panerai 2533 "Frankenstein"