Dredger goes looking for WWII minefield
Lyttelton Port Company says the owners of the world’s biggest dredge, the Fairway, have surveyed the harbour heads for any signs of 10 World War II mines across the entrance.
The Fairway will dredge 2 metres deeper than ever before in the general area where German minelayer, the Adjutant, laid mines in 1941 on a mission which included laying several across the entrance to Wellington Harbour.
Lyttelton Port development manager John O’Dea said the possibility of mines was identified as a risk early on.
Dredge owner Boskalis had carried out a magnetometer survey to identify any large metallic objects such as mines within the dredge area.
‘‘None were found,’’ O’Dea said. ‘‘The port company accessed historic records which indicated the mines were outside the proposed dredge area for stage one.’’
Boskalis said it regularly dredged in areas of the world where unexploded ordnance was present on the seafloor, and it had well-developed procedures to manage the risks.
But naval historian Murray Dear said that although the threat was probably low, ‘‘We just don’t know’’.
‘‘I looked at the dredging plan and it seemed to me the dredge must go over mines five, six and seven,’’ Dear said.
‘‘It depends how stable they are. The electronic fuses will have lost their charges a long time ago but if they took a hard knock ...’’
It was likely the mines had sunk into the seabed or had become covered with silt washing over them, Dear said.
‘‘It is possible that there might be detonation if a mine is struck by a suction pipe drag head. A full mine detonation would very likely cause serious damage to the Fairway,’’ Dear said.
In 2010 divers carrying out a Royal New Zealand Navy visual survey of the seabed off Lyttelton Harbour were unable to find the mines over the square kilometre of the search, and presumed they had sunk into the mud.
Dear has written an account of the Adjutant’s activities from the log books and diaries of the crew who noted comings and goings of ships in the darkness, and the lights of Lyttelton and Wellington in 1941.
‘‘They are all burning peacefully. A searchlight at Godley Head directed towards Baleine Point bars the main approach to the harbour,’’ the Adjutant’s Lieutenant Karsten wrote in his logbook.
‘‘I want to lay the mines at Wellington tonight before the harbour is warned – and, so far, Lyttelton has not reported anything.’’
Karsten and LieutenantCommander Hemmer were concerned about the deteriorating motor on the Adjutant which developed a loud knocking noise.
But they succeeded in laying the mines at Lyttelton and then Wellington before rendezvousing with another German vessel near the Chatham Islands and scuttling the Adjutant – making it the only German vessel sunk in New Zealand waters. Karsten and Hemmer won the Iron Cross for the minelaying operation.
The only Kiwi killed by gunfire in New Zealand waters in World War II was fisherman James Brassell who was returning to Lyttelton when an artillery shell was fired over the bow as a warning but hit the boat he was in, the Dolphin.