Although less precise than the Shackleton's main ASV.21 search radar, it could give a greater detection range,[1][2] provided that the target was emitting.
As these boats could now run continually submerged, without even needing to snorkel, they were increasingly difficult to detect by previous methods, such as Autolycus or search radar.
The external antenna for Orange Harvest was the distinctive white dielectric 'spark plug' carried on the upper surface of the Shackleton.
The Shackleton did carry HF antennae, but these were supported by two small metal masts, just ahead of Orange Harvest.
The structural fitment for Orange Harvest was a metal plinth built into the fuselage, at approximately the previous dorsal turret position.