The Link Crab had another less well known application. It acted as the "submarine" for the RAF's Stage 2 Sonics Trainer. Stage 2 simulated the Sonics 1C sonobouys used by the Shackleton and Nimrod MR1.
The aircraft operated a few miles offshore and transmitted the position of the simulated sonobouys it dropped to the Stage 2 operators. They positioned the "cans" on the rails above the plotting table in the correct relative positions. A wire was pulled from the base of the "can" and attached to a Link crab on the plotting table below. The bearing and distance was calculated from the orientation of the wire and converted to a sonobouy signal which was transmitted to the aircraft. The cables connecting the "cans" to the transmitters can be seen going up to the aerials on the roof. The "crab" was driven by the Stage 2 operators and produced a trace on the plotting table. You can see the umbilical cable in the photo. The plot was annotated with the sonobouy positions, weapon release points and assessments of attack accuracy. The plot was then collected by the crew for the debrief. Stage 2 had its limitations, but actually worked quite well and provided useful training.
YS