After the 2nd World War, wreck search and investigation had top priority to ensure the safety and efficiency of navigation in the few navigation channels that had been cleared of mines. Before the war, wrecks close to the coast used to be mapped by the Waterways and Shipping Authorities, with deployment of divers for closer investigation in individual cases. Wrecks located in deep water outside the coastal waters, which did not pose a hazard to shipping, were recorded but not monitored routinely. Their position, like that of all other wrecks, was notified in the notices to mariners („Nachrichten für Seefahrer“ – NfS) which are used to correct nautical charts. However, many ships were lost without their position having ever been identified in systematic surveys of large sea areas as it is common practice today using latest state-of-the-art equipment.
When ship sizes began to exceed 100,000 tons, the need arose to record and monitor each underwater obstruction – an effort from which net fisheries benefitted as well. The traditional wreck searching method was to tow ropes across the seabed which were fastened to two ships. This method continued to be used also after the introduction of the first echosounders because it was capable of locating small or very narrow objects on the seabed which were not detected by echosounders.
Wreck search has become easier after the development of sonar equipment during the last World War, which was used to locate submarines. When searching for unknown underwater obstructions or investigating known obstructions, the area is first scanned by a sonar beam.
After an underwater obstruction has been located, a marking buoy is set and a diver is deployed to investigate it in detail. Via telephone cable, the diver reports the investigation results to the ship’s master. After a dive the diver normally prepares a
sketches of the underwater obstruction.