Active sonar, for aircraft purposes still largely associated with dunking, suffers less variability but often has less range. […] Development of both dunkers and sonobuoys continues towards lower frequencies, implying bigger arrays, and deeper deployments.1986, Jane's Defence Weekly, volume 6, page 1285:
Then they drop the dunker into the water and spin it around a few times so you end up upside-down.2013, Philip Kaplan, Naval Air: Celebrating a Century of Naval Flying, page 179:
Dunker
noun
Etymology From German Tunker (“immersionist”), related to dunk (“dip, submerge”).
1
One of a religious denomination whose tenets and practices are mainly those of the Baptists, but partly those of the Quakers.