The survey ship
The ship used for this expedition was originally a deep-sea trawler. Now adapted and renamed MV Northern Horizon , she has been on some high profile expeditions, including three led by Dr Bob Ballard, of Titanic fame.
Northern Horizon is a dynamically positioned (DP) ship. This means that a complicated system on board works out her position with reference to a global satellite at the same time as measuring the winds, tides and any other factors that cause the ship to move. Using this information, a computer sends signals to the ship's finely-tuned controls, so they adjust to keep the ship in exactly the same position.
At the stern, two tubes run through the ship from one side to the other. If, for example, the ship moves to the right, a propeller in the tube forces the vessel back to the left - and vice versa.
At the front is a white gill thruster, which can direct jets of water in any direction to help control the position of the ship, and keep it in a particular position or mode.
Side scan sonar.
Sound waves pass easily through water and this is what the team use to search for the wreck. A vehicle, the Ocean Explorer 6000, is suspended from the survey ship and allowed to sink towards the seabed. It is then towed along by Northern Horizon.
Mounted on this towfish is a unique side scan sonar that sends an acoustic pulse out sideways - at 90 degrees to the direction the vehicle is moving - through the water. As these beams of sound bounce back, the echoes are transmitted by cable to the ship on the surface, where computers translate the impulses into a picture of the seabed and any objects on it.
Using a very low search frequency, this sonar can cover huge swathes of the seabed in a single pass making it much more likely that the expedition will find what they are looking for.
Once the wreck has been found, it's time for the ROV to take over.
The remotely operated vehicle (ROV)
No human being could dive deep enough to explore the wrecks of the ships that went down in this epic battle. Instead, Magellan 725 , an ROV is sent to the seabed.
ROV Magellan 725
Built to withstand the massive pressures at these depths, the ROV is connected to the survey ship by thousands of metres of reinforced steel umbilical cable. This 25 horsepower vehicle propels itself according to instructions from a pilot on the survey ship using a joystick like those used to fly fighter planes.
Mounted on Magellan 725 are specialised lights and cameras, which will be used to 'see' and create a record of the wreck.
The ROV has two arms that are also controlled from the survey ship. These can be used to probe the wreck but on this expedition nothing will be touched. Their only role is to place a plaque at the site of the wreck to commemorate those who lost their lives in the battle.
Not only is it very dark at 3,000 metres but water gives everything a bluish tinge.
One aim of this expedition is to take pictures that are good enough to broadcast, so the lights must counteract the problems of filming underwater. To complicate matters, particles in the water reflect any light that's shone on them, creating bright spots that would ruin photographs.
It is very difficult to get the lighting right but, at a cost of $28,000 per system, the lights being used on the Hood v Bismarck expedition, will counteract the effect of the particles and correct the colour problem, enabling the team to send back the best images ever seen at such depths.
This expedition is using the most advanced cameras . They are encased in strong titanium so they will not be crushed by the extremely high pressures.
As well as all the features a sophisticated camera team would expect on any television project, the cameras have an optical lens system that corrects the distortion caused by water. They are also designed to work at very low light levels. These amazing cameras produce images of the same quality underwater as they do on deck.
The cameras are bolted to the ROV and are operated from inside the survey ship through the ROV's control system. They send images up a fibreoptic cable to the ship, where operators look at them and adjust the cameras and the lights to obtain the best possible picture quality to send on to our TV screens. The messages are transmitted so fast that the cameras respond instantly to any adjustment made from 3,000 metres above them.