Naval divers then investigated the device and found a Lobster (nicknamed Lionel) had made his home in the bomb. The device tried to coax Lionel out but got a nip for there troubles.
The bomb squad then set charges to the mine with Lionel still inside, they then set up a 1,000m cordon around the bomb and blew it up.
The explosion sent a 50ft plume of water shooting skywards and shook the nearby town of Swanage. Lionel did not survive.
A spokesman for Portland coastguard said:
It seems that the lobster made his home inside the mine, in the hole where the parachute would have come out.
We don't know how long he was living in it but we named him Lionel as soon as we realised he was there.
The mine was spotted by divers who took photographs of it to show us.
It is a Second World War mine, which was dropped by the Germans and has lain there unseen for over 60 years.
Overnight, we arranged for the bomb disposal unit to come and look at it. When they saw what it was, they cleared a 1,000m zone around and detonated it.
It sent up a huge jet of water - it did look very dramatic. We received three 999 calls from people worried about it.
Unfortunately, the bomb disposal unit have a job to do and it wasn't possible to save Lionel.
We've had a moment's silence for him though, because he was no doubt blown to smithereens in the explosion
Fiona Smith, a crustacean expert at the Sealife centre in Weymouth, said:
Lobsters like to make their homes in crevices and rocky areas.
When they've made a little cave for themselves they are quite territorial and won't let anything else near them.
Animals will colonise anything they find on the seabed and its not at all surprising that a lobster would live in a mine like this.
Obviously no other creature was brave enough to go near it because they do get a bit aggressive.
In this case, if something or someone appeared in front of Lionel's home, his pincers would be up immediately to defend it.
He would be trying to protect his area and himself against people he probably thought we trying to eat him.