Submarine Communications Scope for Indo-US Cooperation

By Sayan Majumdar


New Delhi, 25 February 2005

Submarine communications is an area where the US Navy retains an undisputed supremacy in support of her strategic submarine fleets. Now new information made public, makes this area one of the prominent spheres of Indo–United States 

technical and military cooperation.

Through the decades the Indian Navy was perhaps the pioneer among the Services in strategic thinking and anticipated its value as a potential key component of India’s emerging, albeit closely guarded nuclear-doctrine. It was apparent from the outset that nuclear-powered ballistic missile armed submarines (SSBN) would constitute the most reliable element among assured retaliatory nuclear-strike platforms, for their inherent “stealth” attributes, for being mobile, submerged and out of reach of most electromagnetic frequency bands for detection. A similar view was forcefully held by the legendary Russian Admiral of the Fleet Sergey Georgyevich Gorshkov, and knowing his personal influence on the Indian Navy’s strategic thinking and formulation, this was hardly surprising.

Presently, decades later not only an Indian Navy SSBN in the shape of Advanced Technology Vessel (ATV) is gradually taking shape, as an interim measure, if few more or less reliable yet radical media reports are to be believed, the strategic and perhaps the nuclear-punch is being incorporated in conventional-powered hunter-killer submarines (SSK) in the shape of specific BrahMos supersonic cruise missiles. The potential is also inherent in possible Indo-Israeli developments in missile technology, especially in areas of Inertial Navigation Systems (INS) and terminal guidance. Yet to be really effective in the strategic sense, the submarines in the area of situational awareness, remain inherently weak because of their “isolationist nature” and need to be contacted and commanded by National Command Authority (NCA), to issue launch orders, the absence of which cripples the formidable strategic platform and renders it impotent.

No wonder the Indian Navy attached high priority to submarine communications even decades ago and subsequently anticipated the importance of Very Low Frequency (VLF) underwater transmissions instantaneously. As part of an ambitious naval modernisation program, during the mid-1980s the Indian Navy had constructed a VLF broadcasting station in Tamil Nadu. Although not publicly declared, it was reported that the United States, the undisputed leader of submarine communications actively collaborated in the project, which was completed in September 1986. This facility needs to be viewed as an “initial step” in the quest of development of underwater Very Low Frequency/Extremely Low Frequency (VLF/ELF) and laser communications for effective coordination of the submarines with the Indian NCA.

The operational VLF facility is used by the Indian Navy to communicate with its SSK fleet of Russian Kilo Class and German Type 1500, with trailing communication buoys at periscope depth of 10 to 20-metres. After the nuclear-powered ATV become operational, the VLF facility will permit Indian National Command Authority to issue launch orders to the submerged ATVs at periscope depth. VLF waves propagate to almost a quarter of the globe away and are generally immune to atmospheric disturbances caused by nuclear detonations. Extremely Low Frequency (ELF) waves on the other hand can penetrate to depths of 100-metres but a huge overland infrastructure needs to be built up with at least 80-km long antennae. In this context, as far back as 1986, researchers from the Defense Electronics Applications Laboratory, Dehra Dun, after reviewing the effects of nuclear radiation and EMP on VLF/ELF communication systems,, concluded that "ELF radio communication was the only reliable means which could withstand the effects of a nuclear holocaust and was least disturbed by the EMP generated by nuclear explosion". Subsequently classified research and development in these areas was carried out by National Institute of Oceanography, Goa, Indian Institutes of Technology (IITs) Madras and Bangalore, and Defense Electronics Applications Laboratory, Dehra Dun –– although the system in principle relies on fixed terrestrial infrastructure and thus was vulnerable to enemy strikes.

However on the negative side, the small bandwidth of VLF transmission limits the rate of transmission of data, usually allowing only the operation of slow Teletype messages. Moreover the large terrestrial and static VLF/ELF facility would be vulnerable to enemy strikes as even if the facilities are shifted deep underground in “hardened” shelters, the vital and critical communication antennae would have to be located above ground and would remain vulnerable.

Thus Indian Navy is left with no other option but to develop, ideally with United States assistance, an airborne VLF transmitter similar to the United States Navy (USN) “Take Charge & Move Out” (TACAMO) to ensure survivability of its VLF facility and thus retaining the critical sub-surface nuclear-punch. For TACAMO missions the USN initially utilised the EC-130A/Q Hercules platforms with a powerful 200-KW transmitter providing the VLF transmissions through a 10-km long trailing wire antennae with a drogue parachute at the end. During transmission the aircraft maintained a flight-profile in a continuous tight circle, which resulted in over 70-percent of the wire hanging straight down and acting as a relatively efficient vertical antenna.

The undisputed lead of United States in the area of VLF TACAMO technology is forcefully represented by the present Electro Magnetic Pulse (EMP) hardened E-6 Mercury airborne platform of the United States TACAMO Communications System providing survivable communication links between the United States NCA and Strategic Forces. A derivative of the classic commercial Boeing 707, in-flight refueling facility ensures E-6 mission ranges of over 6000-nautical miles and endurance of up to 72-hours, thanks to four economical CFM-56-2A-2 high bypass ratio fan/jet engines with thrust reversers.

A further enhancement in the form of E-6B fulfils both TACAMO and Airborne National Command Post (ABNCP) missions by incorporating a subset of United States Strategic Command (USSTRATCOMM) EC-135 ABNCP equipment into the E-6 platform along with battle staff positions as determined by USSTRATCOMM (J36). The result is a formidable dual-mission aircraft capable of fulfilling either the E-6A mission or the airborne strategic command post mission (“Looking Glass”?) and is equipped with an Airborne Launch Control System (ALCS) capable of launching United States ICBMs. With at least a pair of E-6 always airborne the mobility and flexibility of E-6B provides a survivable Command, Control and Communications (C3) force management for the United States NCA via multiple frequency-band communications, an aspect the Indian Navy should emulate at least in principle and policy to ensure survival of its hitherto limited strategic arsenal.

Meanwhile in a series of technological breakthroughs attention has shifted to laser based underwater communications. There is an optical window in the blue-green part of the laser spectrum, which enables transmission to penetrate the ocean to substantial distances to depths of 500–700-meters. Power requirements are considerable and the system at least presently cannot be installed in artificial satellites. Thus as a tactical improvisation the laser is made ground based, preferably mobile, in perfect conjunction with a space based mirror with adaptive optics being used to produce a cohesive beam. Significantly, data transfer rate will be with “unrestricted speed” somewhat 300 times greater than ELF system. Laser communications will assume priority significance if they become capable of down-linking satellite imagery of enemy ballistic missile deployment and launch, in friendly submerged submarines to ensure assured retaliatory strike.

In India by the early 1980's work proceeded on laser communication links from the air and ground in a joint project at the Ocean Engineering Centre and the Laser Communication Laboratory, IIT Madras so that by 1985 an experimental facility for measuring the attenuating effects of the ocean surface on laser beam penetration was already in operation. It was concluded "that (hindrance by) ocean waves were not a serious drawback in a laser communication link, as long as the laser had sufficient power to penetrate the atmosphere twice and penetrate ocean water for a distance up to several hundreds meters". Measured values of attenuation coefficients, for ocean waters collected from the Arabian Sea and the Bay of Bengal, were presented in due course with the region of minimum attenuation for pure particle-free sea water, were found to be 450–500-nm.

No wonder, United States assistance in this sphere will prove to be decisive as the effective combination of nuclear submarines and underwater VLF/ELF and laser communications will make our sea based nuclear deterrent optimally effective and serve as an assured deterrence in any “emerging Nuclear Scenario”.  

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