They're the ones you call in when the other searchers have given up.
They're the Royal New Zealand Navy autonomous underwater vehicle (AUV) team and this week they have been carrying out a joint search exercise with the Police National Dive Squad on Lake Taupō.
The 15-strong team from the HMNZS Matataua's Littoral Warfare Unit have teamed up with the Police National Dive Squad to improve procedures for search operations in fresh water.
Based out of Devonport, the Navy unit brought down their 7.5m boat the Pathfinder and a Remus AUV they call "the fish". It is capable of electronically detecting underwater objects and relaying sonar images back to a shore operator.
In their work assisting the police, the team are called in as a last resort by HQ Joint Forces New Zealand when Land Search and Rescue or police have exhausted all efforts to find a missing plane, boat or missing person.
Petty Officer Greg Carter said the HMNZS Matataua AUV team would get called up two or three days after someone has gone missing in the water. He says the team brings highly sophisticated sonar technology to give a photograph-like visual of the lake floor.
"We do quite a bit of work with the Police National Dive Squad. It's good training for us to interact with other government agencies."
The brief for the exercise was that someone had gone missing off the lake front at Four Mile Bay. They were seen walking into the lake and may have been were holding a weapon.
The unit ran the AUV in a 300m by 400m grid pattern, at an altitude of 3m from the lake bed for about one-and-half hours.
Then it was the job of hydrographic survey specialists Leading Hand Tim Sherriff and Able Rating Ana-Marie Conroy to view the sonar playback, noting contacts of interest. The playback very clearly picked up what could have been a firearm and a missing person.
Chief Petty Officer Quinn Harris said the exercise was a great opportunity for the unit to put together a mission based on the information provided. The AUV unit provides HMNZS Matataua with a search function.
"There are three scenarios we encounter. There is a sunken vessel or kayak, and a missing person. Or there is a missing person and a firearm."
Carter says they have a young team at the moment and the training will come into use when the unit is deployed overseas for the second element to its work - mine counter-measures.
"It's good to benchmark against other countries. We learn from them and they learn from us."
Command Warrant Officer Norman Leaming explains that in a wartime scenario, the defending country will mine their ports.
"There will be one way in for vessels. Our role will be to use sonar to search for mines. Another team from the Navy will dispose of these mines."
The final step in the mission was to carry out a post-mission analysis and provide a written report to the Police National Dive Squad.