It's a tad difficult to achieve an RVR (Runway Visual Range) in excess of 1,500m with a runway length of only 694m!
A few years ago I was at ISC when the sea fog came in. The DHC6s and BN2 cancelled their departures. ATC told me their minimum visibility for take off was 3km. At the time it was varying between 600m and 1000m. All these figures were met visibility not RVRs.
The S-61 was able to continue operating in that visibility.