A small armada of specialized planes and vessels is taking part in the frantic search for the tourist submersible missing in the North Atlantic with five people aboard.

They include submarine-detecting planes, teleguided robots and sonar listening equipment to help scour the ocean for the sub, which had been on an expedition to visit the wreckage of the Titanic.

Here is a look at this flotilla.

At the start of the search on Sunday, U.S. and Canadian military planes were sent to the site of the Polar Prince, the mother ship that deployed the submersible called Titan hours earlier.

Several U.S. C-130 planes are scouring the surface of the sea visually and with radar. Canadian P-3s — maritime patrol planes — have deployed sonar buoys to listen from the surface of the ocean. A Canadian P-8, a submarine-chaser that can detect objects under water, has also joined the search effort.

It was Canadian P-3 that detected underwater noise Tuesday that provided the first glimmer of hope that the people on the Titan might still be alive, the U.S. Coast Guard said. Officials said Wednesday that the noises were detected for a second consecutive day.

"With respect to the noises, specifically, we don't know what they are, to be frank with you," Coast Guard Capt. Jamie Frederick said at a briefing Wednesday. "...We're searching in the area where the noises were detected."

Frederick said the team has two ROVs — remotely operated underwater vehicles — "actively searching," plus several more are on the way and expected to join the search operation Thursday.

Deep Energy, a ship that lays pipe on the seabed, has rushed to the scene and sent robots into the water. A Coast Guard photo shows the ship at sea, its deck packed with huge pieces of heavy equipment.

Three other ships arrived on the scene Wednesday morning. Frederick said the team had five "surface assets" on site as of Wednesday afternoon, and another five were expected to arrive within the next 24 to 48 hours.

The Canadian Coast Guard contributed the Atlantic Merlin, which has an underwater robot, and the John Cabot, a ship with side-scanning sonar capabilities to capture for more detailed images.

The third is the Skandi Vinland, a multi-purpose vessel dispatched by the Norwegian oil services company DOF. It has deployed two underwater robots.

A vessel called L'Atlante, a research ship belonging to France's National Institute for Ocean Science, is scheduled to arrive Wednesday evening. It boasts a robot called Victor 6000, which has a five-mile umbilical cord and can dive more than far enough to reach the site of the Titanic wreck on the seabed, more than two miles down.

The U.S. Coast Guard says four other vessels are expected to arrive, including the Canadian military ship Glace Bay, which features medical staff and a hyperbaric chamber used to treat people involved in diving accidents.

A Canadian research vessel lost contact with the 21-foot sub an hour and 45 minutes into its dive Sunday morning about 900 nautical miles off the coast of Cape Cod, Massachusetts. It had been expected to resurface Sunday afternoon.

In:
• RMS Titanic
• Submarine
• United States Coast Guard
• Canada