Mine clearance vessels are now working to create a map of the seabed off the west coast to document it.
"The Swedish Armed Forces have a commission in this particular case to map the seabed off the west coast. We haven't had a major exercise here for some time, so it's a good thing that the SWENEX is on the west coast this year," says Fredric Leufstadius, second-in-command on HMS Koster.
"Many people probably imagine that it's not very difficult to find things under the surface, but in fact the seabed looks similar to the land surface. There are hills and valleys, rocks and stones, vegetation and many other features that make it difficult to find mines or even a submarine." The waters around the Gothenburg archipelago hold another challenge, too.
"The salt content of the water is quite a lot higher than on the east coast. Ships' sonar can't easily present a clear picture of the bottom due to the salt and temperature. Sonar is the technology we use to search the seabed," says the second-in-command.
Ensuring safe passage for shipping
A mine is fairly easy to drop without being detected, and does not require advanced equipment. If a port such as Gothenburg were to be closed, it would put a lot of pressure on society since about 90% of Swedish imports and exports are by sea.
"In 2005 a fishing vessel had a mine in its trawling net and unwittingly took it into Gothenburg port. The port and parts of the city of Gothenburg had to be cordoned off. The mine was dealt with by the Swedish Armed Forces, who transported it out to sea and disposed of it safely.”
The task for mine-sweepers in this exercise is to ensure that the shipping routes into a port are safe. It is a time-consuming job and there are no margins for missing threats. Swedish defence relies heavily on mapping the seabed.
When the speakers on board crackle again at 04:45, all 28 of the crew are now at the ship's battle stations. "Attention all hands! We are drawing fire from nearby islands. No personnel are injured". There are many hours of the exercise left and the men are really on their toes. There will no doubt be another awakening in store for the crew from the speakers calling out "Battle stations!".