Finding October

Two teams, blue and red, play a game in which Red has a submarine we call October, as in Tom Clancy's novel The Hunt for Red October. The Blue admiral is trying to locate the submarine using helicopter-deployed probes that are dropped in the water (see the Figure here). A probe will detect the submarine if the probe's position is within some distance d of the submarine, returning a message either "detected within d" or "not detected within d."

The Blue admiral's goal is to know the position of the submarine within a distance x over a time period T, using as few probes as possible.