Following a warship in peacetime differs from attempting it during war, when the ship can engage the drone revealing its position. The drone's purchase price is only part of the calculation because the location information it supplies can be much more valuable. The Italian Navy's use of 76 mm guns is offered as a response to small drones at range. This connects gun defense with protecting a ship's location.
Notable Point · 3:29:31-3:30:24
The information supplied by a tracking drone
A tracking drone's value includes the ship-location information it supplies, which changes the economics of defending against it.