Anti Submarine Warfare

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HMS Andromeda was, first and foremost, a submarine hunter. That was what she was designed to do, what she was built to do, and what the Cold War demanded she be ready to do every day of her twenty-five years in service.

Why It Mattered

Throughout the Cold War, the Soviet submarine fleet represented the single greatest threat to NATO's survival. If war had come, Soviet submarines would have attempted to cut the Atlantic supply lines between North America and Europe, the same lifelines that German U-boats had tried to sever in two World Wars. The Royal Navy's job was to stop them, and the Leander-class frigate was the ship designed to do it.

Andromeda spent her career in places where a Soviet submarine threat would have materialised. Every patrol, every exercise, every deployment was shaped by one question: Can we find them before they find us?

As Built (1968–1977)

When Andromeda commissioned in December 1968, she carried a layered anti-submarine warfare capability built around detection, attack, and airborne reach.

Her sonar suite was her most important equipment. The Type 184 medium-range search sonar was her primary tool for detecting submarines , an active, hull-mounted sonar that could locate contacts in the waters ahead and around the ship. This was supported by the Type 162 bottom search sonar, used for classifying contacts sitting on or near the seabed, and the Type 170 attack sonar, which provided precise targeting data for her main anti-submarine weapon. She also carried a Type 199 variable depth sonar (VDS), towed behind the ship on a cable and lowered beneath the thermal layers that could hide a submarine from hull-mounted sets. The VDS was a critical capability — it meant Andromeda could search depths that would otherwise be invisible to her.

Her primary anti-submarine weapon was the Limbo - officially the Anti-Submarine Mortar Mark 10. This was a triple-barrelled depth charge mortar mounted aft in a well on the quarterdeck, capable of throwing a pattern of three charges out to around 1,000 yards in any direction around the ship. Mortar Mk10  was loaded and fired automatically with the crew under cover, stabilised for pitch and roll, and directly slaved to the Type 170 attack sonar. The two systems worked as one: the Type 170's three operators maintained sonar contact with the target and aimed the weapon in bearing, range, and depth. When the target was in range, the mortar fired on command, placing its charges in a triangular pattern around the submarine to create a devastating convergent pressure wave. It was a proven and effective weapon, the final development of forward-throwing anti-submarine weapons that stretched back to the Hedgehog and Squid of the Second World War.

Her other key asset was her helicopter. Andromeda carried a Westland Wasp in a hangar and flight deck aft. The Wasp could be armed with Mark 44 or Mark 46 homing torpedoes, Mark 11 depth charges, or even a WE.177 tactical nuclear depth bomb, and extended the ship's anti-submarine reach far beyond what her own weapons could cover. A submarine detected at distance by sonar could be prosecuted by the helicopter long before Andromeda herself was close enough to use her Mortars. The helicopter transformed a frigate from a ship that had to close with its target into one that could strike from miles away.

Sonar Configuration from the Builders 1968

• 184 Medium Range Detection Sonar
• 170 Short Range Fire Control Sonar for the Mortar Mk 10
• 199 Variable Depth Sonar (VDS) for picking up submarines hiding in the thermal layers
• 162 Bottom / Seabed classification of targets

This configuration indicates that, for the period, Andromeda was a very advanced and capable submarine hunter.

Some Royal Navy sources suggest that earlier Leander-class frigates could have carried Type 177 instead of Type 184, but the public sources currently available for Andromeda herself point to Type 184 as her as-built search sonar. 184 / 184M was introduced into Royal Navy service in 1964, and Andromeda was launched in 1968.

After Modernisation (1977–1993)

Between November 1977 and December 1980, Andromeda underwent a major reconstruction at Devonport that fundamentally changed her capabilities. She was the first of only five Broad-Beamed Leanders to receive the Sea Wolf conversion,  a programme that cost around £70 million per ship and turned her into one of the most capable frigates in the fleet.

The mortar was removed and the mortar well plated over, and with it went the Type 170 attack sonar that had controlled it; the two systems had been inseparable since the day she was built. In their place, Andromeda received two triple STWS-1 torpedo tubes, each capable of launching 324mm lightweight anti-submarine torpedoes. These were a significant upgrade, faster to deploy, effective at greater ranges than mortar, and the torpedoes could pursue a submarine autonomously once launched, homing on the target without further guidance from the ship.

Her sonar suite was overhauled. The Type 184 was replaced by the Type 2016 long-range search sonar, a far more capable set that gave Andromeda significantly greater detection range and better classification ability. The Type 162 bottom search sonar was retained, providing continuity in seabed search operations.

The Westland Wasp was replaced by the larger, more capable Westland Lynx. The Lynx was a transformative aircraft for anti-submarine warfare, faster, with longer range, better sensors, and the ability to carry more advanced torpedoes. The hangar and flight deck were enlarged to accommodate it. With the Lynx embarked, Andromeda could detect, track, and attack a submarine at distances that would have been unthinkable a decade earlier.

The modernisation also gave Andromeda a completely new radar suite , Type 967 air-search, Type 968 low-level air warning and surface search, Type 910 fire control, and Type 1006 navigation radar,  along with a sextuple Sea Wolf surface-to-air missile launcher and four Exocet anti-ship missiles. Every existing radar was stripped out and replaced. She emerged from Devonport as a true multi-role warship, but her anti-submarine capability remained at her core.

Andromeda also received the Type 182 towed torpedo decoy, a significant addition to her defensive capability. Manufactured by Graseby, this was an acoustic device stowed on the quarterdeck and lowered astern by davit when a torpedo threat was detected. Once in the water, it transmitted acoustic signals designed to seduce incoming torpedoes, both active and passive homing, away from the ship, making itself a more attractive target than Andromeda. In a Cold War where the submarine threat was primarily about torpedoes, the Type 182 closed a critical gap: Andromeda could now hunt submarines and defend herself against their weapons at the same time. It was the difference between being a hunter and being a survivor. 

The Falklands: Goalkeeper

When Andromeda sailed south in 1982 as part of the Bristol Group, she was the first of only three Sea Wolf-fitted frigates available to the Royal Navy, and her role was critical. She was assigned as close escort to the aircraft carrier HMS Invincible, acting as the last line of defence,  the "goalkeeper", against both air and submarine attack.

Throughout the conflict, Andromeda conducted anti-submarine warfare patrols around Invincible, screening the carrier against the threat posed by the Argentine submarine San Luis, which was known to be operating in the area and had already attempted torpedo attacks against British ships. Her Lynx helicopter flew continuous anti-submarine sorties, searching ahead of the task force and responding to sonar contacts. Her Type 2016 sonar scanned the waters around the carrier group for any sign of submarine activity.

It was painstaking, unglamorous, and absolutely vital work. If a submarine had got through to Invincible, the consequences would have been catastrophic. Andromeda's job was to make sure that didn't happen. It didn't.

The Quiet War

Anti-submarine warfare rarely makes headlines. There are no dramatic photographs, no visible explosions, no obvious victories. It is a war of patience, discipline, and technical skill , fought in sonar rooms and operations rooms by people staring at screens and listening to sounds in headphones, often for hours at a time without result.

The men who served aboard Andromeda in her anti-submarine role,  the sonar operators or TAS Rates, the warfare officers, the helicopter crews, the weapons engineers,  were engaged in the central military contest of the Cold War. They trained for it constantly, exercised for it relentlessly, and maintained readiness for it every day at sea. The fact that the war they prepared for never came is not a sign that the work didn't matter. It's a sign that it worked.