Anti-Submarine Air Armament : Decoded by Rear Admiral Dr. S. Kulshrestha (Retd.), INDIAN NAVY

The evolution of a standoff anti submarine warfare solution involving use of aircraft in detecting a submarine at sea and attacking it with depth charges and air launched torpedoes has its genesis in the devastation caused by the German submarines during WWI.

 By Rear Admiral Dr. S. Kulshrestha (Retd.), INDIAN NAVY

Senior Fellow - New Westminster College, Canada

The evolution of a standoff anti submarine warfare solution involving use of aircraft in detecting a submarine at sea and attacking it with depth charges and air launched torpedoes has its genesis in the devastation caused by the German submarines during WWI. The armament carried today by maritime aircraft and helicopters includes, anti ship cruise missiles, lightweight torpedoes, depth charges and bombs. The aim of this article is to focus on anti submarine air armament currently in use by major navies.

Air Dropped Depth Charges. Finland was the first to use air dropped depth charges from its Tupolev SB aircraft in 1942. Subsequently the methodology was adopted by RAF Coastal Command. Later depth charges were designed for aerial deployment and have recently once again come into focus because of the ASW threat in littorals. These can be very effectively utilized for flushing out the lurking diesel submarines. Two depth charges are worthy of mention, these are the MK 11 depth charge of UK and the BDC 204 depth charge of Sweden.

The Mk 11 depth charge was developed by British Aerospace (now BAE Systems) for air delivery from maritime aircraft and helicopters. The Mk 11 depth charge was designed for shallow water operations against submarines on the surface or at periscope depths. It is fully compatible for carriage and release from a wide range of ASW helicopters and fixed-wing maritime patrol aircraft. The Mod 3 version incorporates a 4 mm mild steel outer case and nose section, which is designed to withstand entry into the water at high velocities without distortion. It has been cleared for carriage on Lynx, Merlin, NH 90, Sea King, and Wasp helicopters.

The BDC 204 depth charge was developed by Bofors Underwater Systems (now Saab Dynamics) for air delivery from maritime aircraft and helicopters of the Swedish Navy. It was designed for use against submarines operating in shallow waters or at periscope depth, and in order to cover a wide range of applications was produced in four different weight categories and with different sinking speeds ranging between 5.2 and 6.8 m/s. The depth charge can be deployed in patterns, with different depth charges set to detonate at different depths to achieve profound shock and damage to submarines. The BDC 204 family of depth charges is fitted with standard NATO suspension lugs and their design allows them to be carried as a high drag general purpose bomb or torpedo. They have been cleared for carriage on the Boeing Vertol 107 helicopter and CASA C-212 Aviocar maritime patrol aircraft.

Air Launched Torpedoes : Few of the prominent air launched torpedoes are described below.

Stingray is a LWT manufactured by BAE Systems. It has a diameter of 324 mm, weight of 267 kg, and length of 2.6 m. Its speed is 45 kts with a range of 8 km and its warhead is 45 kg of Torpex. It can dive up to 800 m. Stingray is fed with target data and other associated information prior to its launch, after entering water it searches for target autonomously in active mode and on acquiring the same, attacks it. It is carried by Nimrod aircraft. Stingray Mod 1 is reported to have a shaped charge warhead and improved shallow water performance.

Mk 46 Mod 5 torpedo is the mainstay of US Navy’s air launched lightweight torpedoes. It is manufactured by Alliant Tech systems. It has a diameter of 324 mm, length of 2.59 m, with a weight of 231 kg.It runs on Otto fuel, has a range of 11km with a speed of 40 kts and can dive up to 365 m. It has a PBXN-103 warhead of 44 kg. It has an advanced digital computer control system with a built in logic and tactics for search and re-attack. It has effectively performed in both deep and shallow waters and can attack both the nuclear as well as the smaller diesel submarine. Over 25000 MK 46 torpedoes have been supplied to customers till date. Interestingly the Chinese YU-7 torpedo is said to have been developed from the MK 46 Mod 2.

The Mk 54 Lightweight Torpedo is a hybrid of technologies taken from MK 46, MK 48 and MK 50 torpedoes.  It is supposed to have homing and warhead of the MK50 and propulsion package of the MK 46 torpedo. It has incorporated COTS processing technologies for an advanced guidance and control system. It is stated to have sophisticated shallow water capabilities for littoral threats. It is understood that the MK 54 torpedo has been requested for P8i aircraft by India.

The A244/S developed by WAAS and currently manufactured by the Euro Torp consortium is a 324 mm diameter, 2.8 m long, and 244 kg weight torpedo. It has a cruise/surge speed of 30/39kts, with a range of 6 km and depth up to 600 m. Its Homing head can function in mixed, active or passive modes. It has special signal processing to distinguish target from decoys.

A244/S Mod.3 is the latest upgrade of the A244/S. It has more powerful propulsion battery, with an increased number of cells, which ensures a 50% increase in the endurance of the weapon to13.5 km. It has an Advanced Digital Signal Processor module to counter sophisticated torpedo countermeasures .The homing head has preformed multiple transmission and reception beams and multi-frequency operating capability. It can classify and track several targets simultaneously, and discriminate between the target and countermeasures.

MU 90/Impact is in mass production for 6 major NATO and Allied Countries. The MU 90/IMPACT torpedo is 323.7 mm 'NATO Standard' caliber, 2.85 mm long with a weight of 304 kg.   It is powered by an Aluminium-Silver Oxide sea water battery using dissolved sodium-dioxide powder as electrolyte with a closed-loop electrolyte re-circulation system, the torpedo is propelled by an electronically controlled high-RPM brush-less motor driving a skewed multi-blade pump jet propulsion allowing a continuously variable torpedo speed automatically selected by in built logic of the torpedo. The control and guidance electronics, has embedded operational and tactical software including the signal processing, the data processing and the torpedo guidance algorithms, which enable the MU 90 to continuously self-adapt its configuration and tactics. The inertial system is based on 'strap-down' technology enabling all-attitudes capability including bottom following capability. The warhead consists of V 350 explosive, fully insensitive, shaped charge warhead, with an impact type exploding device, incorporating two mechanical and six electrical independent safety devices.

Low Cost Anti Submarine Weapon (LCAW) A200/A is a miniature torpedo developed by WASS. LCAW has been developed as an intermediary between air launched torpedoes and conventional depth charges. It is a low cost option which provides propulsion and guidance to a depth charge without the costs of a torpedo. The air dropped version A200/A is deployed from aerial sonar buoy dispensers. The weapon is primarily designed to engage targets in shallow water, like midget submarines. The A200/A version has a length of 914.4 mm, weight of 12 kg, and a diameter of 123.8 mm. The warhead is a 2.5 kg PBX shaped charge and the LCAW has an operating depth from 15 m to 300 m. It has a speed of about 18 kts with a range of 2 km.

About The Author: 

Publication Details:

Kulshrestha, Sanatan. "Anti-Submarine Air Armament: Decoded" IndraStra Global 01, no. 06 (2015): JUNE-08. http://www.indrastra.com/2015/06/Anti-Submarine-Air-Armament-Decoded-by-Rear-Admiral-Dr-S-Kulshrestha-retd-INDIAN-NAVY.html. 

|ISSN 2381-3652| https://dx.doi.org/10.6084/m9.figshare.2065311