[danielvf]

They did have compasses, but those do not give you your position. So if you've been flying for four hours at night, with a thirty mph wind, you could be 120 miles away from where you planned on being. You need some way of getting an absolute position, which these provided.

[astrodust]

Windspeed is not unlike ocean currents, but since the speeds involved are a lot higher than in a boat errors in estimation accumulate way more quickly.