The device was discovered last night during a routine dredging operation ahead of the arrival of the navy’s new aircraft carrier, HMS Queen Elizabeth, next year.
The revelation prompted the evacuation of Gunwharf Quays while the Royal Navy’s elite team of bomb disposal divers towed the bomb from the city.
This morning, a team from the Southern Diving Unit 2, based in Portsmouth, placed explosive charges on the munition before detonating it at 7am.
Commander Del McKnight heads the navy’s Fleet Diving Squadron and said the operation was a success.
He said: ‘The bomb was taken out off the Isle of Wight and gently put on the seabed. We then waited for slack water at about 7am.
‘We put an explosive charge on it to try and sympathetically detonate the explosive inside.
‘It didn’t sympathetically detonate which sometimes happens, it just split the bomb open, rendering it safe.’
He added safety was crucial during the operation and that the evacuation of the shopping precinct was needed.
‘There’s always the possibility when the bomb is being jostled, having been left alone for 60 or 70 years, that it could actuate and the device could go off and blow up,’ he said.
He added people needed to be kept away from the blast radius of the device while it was being transported.
‘Clearly there were a lot of people down in Gunwharf enjoying themselves.
‘What we didn’t want is for their pleasantries to be disrupted by a device going off right next to them,’ Cdr McKnight said.
The device was the second explosive found this month, after a torpedo was unearthed on September 10.
And Cdr McKnight hinted there could be more of the Second World War devices still littering the city’s harbour.
He said: ‘Nobody knows how many there could be still in the water. We had six years or more of bombs being dropped on Portsmouth harbour – the city was a main target for the Germans.
‘I expect that there will be more but as for exactly how many bombs are left I don’t think anybody knows.’