In a rare revelation, the Pakistan Navy announced on November 18 that an Indian Navy submarine was detected and escorted away from Pakistani territorial waters.

While New Dehli has dismissed the report, Pakistani security analysts feel that since the countries are not at war the Indian submarine was on an intelligence gathering mission in and around territorial waters as the date coincided with the first fleet leaving Gwadar port under CPEC.

Anti-submarine expert retired Commodore Zafar Iqbal speculates that the submarine may have been attempting to get near the coast for delivering saboteurs or weapons supply for terrorist groups.

Read more: 'Indian tactics for upping the ante'

Submarines for intel ops?

Submarines are suitable platforms for such mission profiles due to their inherent operational parameters.

As the Indian Navy does not operate a dedicated intelligence-gathering submarine platform, one possibility is that the mission is likely to have been conducted by one of the 15 submarines that form the undersea arm of the navy on paper.

However, the actual operational strength of the Indian Navy’s is less than 15 submarines, as some vessels are undergoing repair and refit. Some of the submarines present in the fleet have served around 75 per cent of their operational life.

The submarine fleet of the navy is based at Mumbai in the west and Visakhapatnam on the eastern coast.

Capability

The bulk of the Indian Navy’s submarine fleet is made up of 10 diesel electric Kilo-class, known in the Indian Navy as the Sindhugosh-class, submarines which were laid down and launched in the 1980s. The navy also possesses a nuclear-powered Akula-class boat, operated on a 10-year lease from the Russian Federation.

The Indian vessel intercepted by Pakistan Navy was most likely a Sindhugosh-class submarine. The boat is said to have a top speed of around 18 knots and can dive to a depth of up to 800 feet. Crewed by a complement of 53 sailors and officers, the submarine reportedly has an endurance of around 45 days.

Diesel electric submarines have the ability to escape detection and continue their mission while making maximum use of battery propulsion and as long as the crew aboard the boat adheres to strict noise discipline. The downside being that the submarines have to routinely surface or at least come to snorkelling depth to charge their batteries.

While the batteries are being charged, the submarine relies on its diesel engines for propulsion and power needs which have a larger acoustic signature.

Vice Admiral (retd) Tasneem, a submarine commander, also validated this and said, "Indian submarine surfaced to periscope depth because it had probably exhausted its battery and had no other option but to surface and recharge its battery”.

What transpired

In this particular case, the Indian submarine was most likely detected while it was snorkelling, making it easier to locate and identify. Anti-submarine warfare (ASW) assets of the Pakistani Navy would have either spotted it or picked up through radar or sonar.

Sonars bounce sound waves of the craft and radars detect subtle disturbances on or below the ocean’s surface. Once a submarine is detected, a cat and mouse game ensues with ASW assets actively searching for the intruding submarine and fixing its location.

If the Indian Navy submarine submerged after its snorkelling run, Pakistan Navy ASW assets would have had a rough location, heading and probable speed. The data would also be immediately passed on to surface units of the navy which would race to the location and join in the hunt.

“She was snorkelling, because she knew she had been detected. So there was no point of further exhausting the battery,” added the admiral.

Using the data available, ASW helicopters and aircraft such as the P-3C Orion and Atlantique would have dropped sonobouys in pre-determined patterns and depths to bracket the submarine. Sonars dipped from helicopters using active sonars pings would also be used.

A source privy to the matter confirmed that the submarine was earlier detected by air assets, with surface units later joining the hunt.

All the activity by Pakistan Navy assets was surely not missed by the Indian submarine, confirming to them that they have indeed been detected.

Once detected, the submarine crew would not have had any other option than to turn around and head towards a friendly port. Pakistani ASW units would have had continuously shadowed the submarine to ensure it was in fact leaving the area.

Submarine and anti-submarine operations are all about training, skill and steady nerves. The side which can hold its nerves in such situations usually comes out on top.