The helicopter shown is an Anti-Submarine Warfare Helicopter. ASW helicopters generally have the ability to detect submarines either Passively or Actively. Passively, sonar-buoys are dropped into the sea and act as ‘microphones’. The returns from these can be triangulated to track submarines.
To achieve this, the helicopters altitude will generally be 1500ft amsl in this role. Unless the winds are very strong salt accretion is minimal. In the active role, the helicopter hovers above the sea and lowers an active sonorhead into the water. The height for this is normally between 40-80ft. The aircraft will stay in this position as long as it takes to establish a 360deg sweep, which is typically less than 5 minutes, or if in contact could remain in the hover for 30 minutes or longer. This process is repeated for the duration of the sortie, which may be up to 2-3 hours.
During this time, the helicopter is experiencing recirculating sea spray. Depending upon the wind / sea state, will determine how much salt accrets (windscreen wipers are required on occasion). The engines experience salt ingestion, which accrets on inlet guidevanes and compressors. As the sortie progresses it is possible to see a reduction in engine performance (the advice for this used to be to find a rain cloud to fly through).
On completion of a days flying over water the engines receive a compressor wash or after a single flight if particularly bad. The airframe will also be washed on a regular basis, perhaps every couple of days. Many bases operating ASW helicopters have dedicated ‘drive thru’ washes. The helicopter will ground taxi over an area with water jets set into the ground and water will spray the airframe and underside of the rotor blades to remove the salt, sometimes known as a ‘bird bath’.