This is of a Coast guard HH52A doing a tuck and recovery manuver in Mobile Bay, Ala sometime I think in the mid 70s. Proceedure was to water taxi at an excessive speed until the nose began to tuck under due to the drag of the water on the hull. Then collective was bottomed and cyclic neutralize to allow the aircraft to recoover. Done to train student to recognize a water tuck so that they did not taxi too fast while on the water (during a rescue) or against a current (as in a river landing). If the tuck was allowed to continue, eventually the blades would contact the water and engine would flame out from water ingestion.
