A new sonar system which is being fitted to six warships at a cost of £160m is being showcased by the Royal Navy on Monday.
HMS Westminster, which has had the sonar installed
The Sonar 2087 system, fitted to the Type 23 frigate HMS Westminster, will be unveiled at Portsmouth Naval Base.
The new technology had been billed as being whale and dolphin-friendly, but tests have revealed it can still cause sea mammals to become disorientated.
The MoD said it would have to be switched off if the animals are nearby.
HMS Westminster had the new technology installed during a recent overhaul at Rosyth in Fife.
'Potential to be harmful'
When unveiling the Sonar 2087 system in 2001, the Ministry of Defence claimed that its advanced technology would no longer leave dolphins and whales
unable to detect rocks or land, making them vulnerable to being beached.
But in September this year, Defence Minister Lord Bach admitted that tests had shown it "has the potential to be harmful to marine mammals".
He said the new system would have to be switched off when whales and dolphins were detected nearby and areas known to be natural habitats for the animals would be avoided by the warships.
A Navy spokesman said: "Westminster is the first warship to get the 2087 system which will help the Navy to better detect a range of stealth seaborne threats including submarines and mini-submarines."
The system was developed by researchers at Southampton University along with the Defence Evaluation Research Agency.