4S_Vega,
After running several anti-ship missions, I think I understand why I had problems initially:
1) It appears to me that the pilot is given 'authorization' to fire before the target is within the harpoon's range. I've gotten authorization at 70 km. I've read that the harpoon's maximum range is 60 km. If the range of the in-game harpoon is indeed 60 km, then the authorization should not be given until within that range.
2) If you fire at a relatively low altitude, 600-700 meters, be selective about the terrain below. If its hilly, wait for the flat lands or until you're overflying sharkville.
3) Fire on the target before you're in visual range. It seems that the harpoon goes through some kind of internal routine before it homes in on the target. Perhaps, harpoons are like a torpedoes in that they have run a short distance before they arm. I noticed that each time I fired a successful harpoon, it would fly straight at first and then make a slight turn to home in on the target ship.
When I fired a harpoon at close range, it usually fell just short of the target. The one time I scored a hit at close range, I think could have been an accident.
In any case, I can harpoon ships now.
Cheers,
Riptide