The simplest and economical way to incapacitate ships and submarines is to damage their underwater hull by use of explosives so that the hull gets flooded with seawater and it sinks. Two types of weapons can damage the underwater hull of a ship — torpedoes and mines. Torpedoes can be fired from ships and submarines or dropped from aircraft. Mines can either be moored at varying depths or laid on the seabed. To ensure that the explosion occurs as close to the hull as possible, torpedoes and mines have mechanisms that avail of the natural characteristics of ships and submarines. For example, ship and submarine hulls are made of steel and steel has a magnetic field. In addition, ships’ propellers make noise.
Mines are basically of two types. Their explosion can be initiated by a ship’s magnetism or by a ship’s acoustic noise or a combination of both. Countermeasures against such serious damage comprise electric cables in the ship that carry exactly the right amount of electric current to minimise its unique magnetic signature. Similarly, if the source of ship noise can be accurately pin-pointed, action can be taken to mitigate that source. When at sea during war, acoustic noisemakers can be used to trigger mines from a distance and avoid damage to the ship.
Underwater ranges therefore meet two basic requirements:-
De-Gaussing Ranges (DG Ranges). These are required for degaussing ships, i.e. demagnetising their hulls to reduce their magnetic signature and thereby minimise the chances of activating magnetic mines. Since magnetic field varies with distance, DG Ranges are of two types — for shallow draught ships and for deep draught ships.
Acoustic Ranges. They are required for noise ranging ships and submarines so as to record their unique noise signature and thereby:-
- Reduce their vulnerability to acoustic mines and acoustic homing torpedos.
- Minimise the range at which their machinery noise can be heard by the passive sonars of adversary submarines.
The Navy’s first DG Range was set up in Bombay harbour during the 1939–1945 World War. It ceased to function after the war ended. After independence, replacement equipment for this DG Range was acquired from Britain in 1951. However, a suitable site for this range could not be found in Bombay Harbour.
In 1964, Goa was chosen as the alternative site and NHQ directed the setting up Deep and Shallow DG Ranges off Goa.
The Deep DG Range
The setting up of the Deep DG Range was finally completed in 1965. The ‘seabed sensors’ were laid off Grandi Island with its associated ‘instrumentation’ set up on top of the island itself. However, this DG Range repeatedly became non-operational due to wave-damage during the monsoons and inability to maintain it.
The Shallow DG Range
The Shallow DG Range at Goa was successfully laid in 1977.
Before this range could be laid, preliminary discussions indicated that DRDO also had commenced a project on noise ranging and on noise mitigation. It became clear that greater consciousness needed to be inculcated amongst dockyard personnel to achieve noise mitigation during ships refits in the Naval Dockyards rather than depending solely on noise ranging.
Meanwhile, the technology of torpedo homing heads and magnetic and acoustic mine initiating mechanisms had improved vastly necessitating a very sophisticated underwater range for ranging our ships and SSK submarines.
A project team was appointed to:-
- Analyse all aspects of noise reduction in ships and submarines.
- Inculcate in the Naval Dockyards the importance of special attention to noise generation aspects during refits of ships.
- Collect as much data as possible.
- Assess the overall requirement and sources of sophisticated equipment for the noise range and indent for those items that had the longest lead times.
- Initiate urgent action on all aspects of noise measurement and noise reduction.
Until 1975, only portable noise ranging equipment was available for carrying out noise ranging.
The Underwater Ranges Project
The Leander Frigate Project of the 1970s and the SSK Submarine Project of the 1980s sharpened the urgency to set up modern DG and Acoustic ranges on which indigenously constructed ships and submarines and minesweepers could be ranged.
In 1983, the Navy decided to set up the Underwater Ranges off Goa comprising an acoustic range and two degaussing ranges.
In May 1985, DRDO formed the Underwater Ranges Project to carry out a feasibility study. The feasibility study report submitted in 1988 recommended setting up the ranges at Bimbade Point in Goa.
Scope of the Project
Based on the feasibility report and numerous amendments after a series of studies, Govt sanction was accorded in 1995 for setting up:-
- A Mine Counter Measures Vessel DG (Magnetic) Range for minesweepers at a depth of 9 metres and at a distance of 1.5 km from the shore.
- A steel ship DG (Magnetic) Range for ships and submarines at a depth of 15 metres and at a distance of 4.5 km from the shore.
- An Acoustic Range for ships and submarines at a depth of 30 metres at a distance of 18 kms from the shore.
For the execution of the project, a computerised Underwater Ranges Facility was set up in a shore office to function as the administrative and technical block and as the field unit of NSTL (Vizag) with a mixed complement of naval, DRDO and civilian personnel.
In 1997, the execution of the Project was contracted to a consortium of ER & DC, Thiruvananthapuram as the ‘prime contractor’ and M/s Thorn of UK as the ‘Principal Partner and System Designer’, to be completed by Apr 2000. The Technical and Administrative complex of the project was completed on June 30, 1998.
The offshore equipment of the DG ranges, including the range cables and sensors were laid at sea by Jan 2000. System installation and on-site acceptance trials progressed till Mar 2000.
During this activity, it was found that fishing/trawling activity had damaged the DG sensors and the underwater cables connecting the sensors to the technical block on shore.
Consequent to the loss of DG Range sensors and interconnecting cables, it became necessary for additional protective measures to be devised and validated before expending additional funds on the project. Trials of protective measures were completed in end Mar 2001.
It took another two year’s monsoons to validate that the protective measures could withstand wave damage and fouling by anchors of trawler.
On satisfactory completion, the Range Technology Centre was inaugurated by Dr VK Atre (SA to RM) on 06 Jun 04 as Naval Underwater Ranges.