Fleet is 3 Boeing 737-300s, where did you get the idea it is now 5?
But back in 1983 their fleet was 7 aircraft. 2 727s and 5 737s.
See History at:
https://en.wikipedia.org/wiki/Our_Airline
I like this comment:
since the entire population of Nauru at this time was about 8,000, the airline was in the extraordinary position of having seating capacity equal to 10% of the Nauruan population