Links with the past

Dec 23, 2002
Author: P&S

A Durban diving company, Propshine Diving has begun removing the first of four anti submarine caissons lining the port entrance channel.

The caissons, built of reinforced concrete, were laid at the outer edges of the port entrance during World War II with anti-submarine nets suspended between them, supported by floats strung across and between the caissons. This was aimed at preventing submerged enemy submarines, in particular Japanese midget submarines or frogmen from entering port.

This threat was considered very real as the Japanese had used midget submarines off Madagascar and the military authorities were aware of the successes of the Italians using frogmen in the Mediterranean. Large I class Japanese submarines were known to be operating in the Indian Ocean, from which both midget submarines and float planes operated. The latter were very probably those that flew over Durban and Port Elizabeth on several occasions in 1942.

The nets were controlled from a small building on the North Pier. Other defences included the positioning of depth charge throwers triggered by magnetic loops suspended in the bottom of the channel.
According to Mr Neville Bransby, managing director of the Durban-based diving company involved, the contract for the first caisson is for six months. He said the caisson had been shattered into several pieces after repeated collisions by ships over the years, and this was complicating the job.

One of the collisions involved the Safmarine container ship SA Winterberg, which hit the caisson in the mid 1980s, breaking off a 400 tonne chunk of concrete in the process, which was deposited it some distance away. Smaller pieces of concrete entered the bulbous bow of the ship, which required a new bow to be fitted before she could sail.

This large separated section is proving difficult to break up into smaller pieces for disposal because of being reinforced with lengths of railway line.

Divers are currently pumping the hollow section of the caisson clear of sand and other debris, and will later use a specially made diamond-tipped saw to cut the 980 tonne caisson into manageable pieces.

Limited underwater blasting will break other sections into smaller blocks of about 90 tonnes, which can then be lifted from the water using the port heavy duty floating crane Indlovu.


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