Could a Torpedo Sink an Icebreaker?

If a torpedo hit an icebreaker, would its tough hull be enough to protect it?
Christopher McFadden

Icebreakers are some of the most robust vessels, apart from warships, afloat. With toughened hulls and powerful engines, these vessels' sole reason for existence is to carve a path through thick sea ice. 

Disasters of the past, like the sinking of the Titanic, clearly show just how treacherous large blocks of ice, like an iceberg, can be at sea. But icebreakers regularly tackle thick ice. Naturally, this leads us to wonder just how hardy these vessels really are?

Could they, for example, survive a direct impact from a torpedo? Let's have some fun and take a look into how the hypothetical scenario might play out. 

What is an icebreaker?

Icebreakers are highly specialized ships that are designed to, well, break through sea ice. These ships have highly modified hulls (and prows) that enable them to cut through ice without getting damaged. Forms of icebreakers have existed for some time, with one of the earliest examples from the 11th-century called a Kochi.

Icebreakers are commonly commissioned to escort merchant ships through thick sea ice, or are employed on their own as research vessels in polar regions. 

what are icebeakers
The Russian icebreaker Krasin. SourceStruthious Bandersnatch/Wikimedia Commons

The thickness of sea ice they can deal with depends entirely on the vessel's size, power, and design. Larger ships, like the Russian 50 Let Pobedy, are capable of dealing with ice as thick as 16.4 feet (5 meters). Smaller vessels, like the RV Polarstern, can handle ice of more modest thicknesses of up to 5 feet thick (1.5 meters).

Such vessels are critical for keeping many polar region shipping lanes open and, as a consequence of their role, tend to operate in some of the most inhospitable places in the world.

what do icebreakers do

The icebreaker RV Polarstern. Source: Hannes Grobe/Wikimedia Commons

What makes icebreakers so special?

Most icebreakers tend to be larger ships, but some smaller vessels can also perform a similar function. Whatever the size, icebreakers tend to share some common characteristics: 

  • Strong Hulls. Since their main purpose is to smash their way through ice, their hulls need to be specially strengthened and reinforced to deal with the additional stress. They're also coated with a low-friction solution that makes it easier to glide over the ice rather.
  • Powerful Engines. Smashing your way through ice takes a lot of power. For this reason, most icebreakers will be powered by diesel-electrical or nuclear power engines.
  • Special Shape. Icebreakers are often wider at the front than the rear. This "teardrop" shape enables them to open up a wide channel through the ice as they cut through. 
  • Smooth Bow. While regular ships tend to have a pointed bow to slice through the waves, an icebreaker's bow tends to be smoother. When the ship hits ice, the smooth bow causes the front end of the ship to ride up on top of the ice. The vessel's immense weight then crushes it from above.
  • Water Jets. Some icebreakers have heated water jets just below the waterline to help eliminate ice.
examples of icebreakers
The icebreaker CCGS Louis S. St-LaurentSource: Verne Equinox/Wikimedia Commons

All of these features work together to help the icebreaker perform its duty. The modus operandi is pretty straightforward and normally involves the ship plowing straight into sea ice, or pack ice. This action causes the ice to flex to either break it outright or cause the ship to "ride" over the top of it, smashing the ice apart using the vessel's sheer mass. 

Most modern icebreaker vessels are so well designed for this purpose, that often the act of breaking the ice doesn't noticeably alter the ship's trim (its angle in the water along its waterline). 

What does a torpedo do to a ship?

Torpedos are devastating weapons designed to explode on impact against, or in very close proximity to, the hulls of surface vessels or submarines. While early examples were fairly basic pieces of kit, modern torpedoes contain highly sophisticated electronics (like passive sonar), and other devices for self-guiding or remote control, stealth, and payload detonation.

Generally speaking, older torpedoes deal damage through the detonation of the weapon's explosives directly against a target's hull, in the hope of punching a hole right through it. This, in theory, will allow water to flood the ship, eventually causing it to sink. 

It often takes more than one direct hit to sink a ship. In fact, there are some examples of warships, like the Japanese battleship Musashi, requiring several direct hits before finally keeling over.

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japanese battleship musashi
The Japanese Battleship Musashi, circa 1944. Source: Lieutenant Tobei Shiraishi/Wikimedia Commons

After the conclusion of World War 2, the technology behind torpedos continued to evolve. In part, this was driven by the need to find ways to circumvent torpedo defense strategies like torpedo belts. In addition, as defensive anti-aircraft capability improved, the planes launching torpedoes needed to do so from higher altitudes and from further away in order to survive. This made it a lot harder to score a direct hit, let alone several direct hits.

Rather than being simple hit-and-explode on impact devices, designs were eventually developed to enable the torpedo to explode just below the target vessel. This would critically weaken the ship's keel, fatally wounding the ship. It could even split the ship in two, thus "breaking its back".

Modern torpedoes, like proximity fused torpedoes, tend to come in one of two types: thermal and electric. The former uses a special fuel, like OTTO Fuel II, which can be burned without an external oxygen source, to power gas turbines or axial piston engines which propel them at speeds in excess of 60 knots (110 kph+). Other chemicals, like Hydroxylammonium Perchlorate (HAP), can also be injected during fuel combustion, to provide even higher rates of speed. 

Electric torpedoes are generally slower but have other advantages (and disadvantages) over thermal torpedoes. 

modern torpedoes
Torpedo and torpedo tube aboard the French submarine Argonaute. Source: David Monniaux/Wikimedia Commons

In either case, modern torpedoes use a mixture of onboard sonar and a "command wire" or fiber optic cable to establish a data link with the fire control system. The process behind this is pretty sophisticated, and out of the scope of this article, but needless to say, modern torpedoes can be very tough to detect and evade. 

With modern torpedoes, detonation tends to occur either as a consequence of impact (like traditional torpedoes) or, often, about a meter away from the target area of the hull, called the 'kill box.' This is achieved using pre-programmed data combined with on-board sonar, or instructions from the fire control relayed through the command wire. 

The torpedoes are directed to the part of the ship that is very hard to adequately protect, and, what's more, damaging this part of the ship can result in the ship's own weight working against itself – as you'll see in a moment.

Proximity fused torpedoes tend to damage ships in three waves. The first is the actual detonation. This creates a pressure wave that results in a giant air bubble under the ship. As the bubble rises, it lifts the ship out of the water, creating massive stress on the ship's hull. When this bubble inevitably dissipates, the ship then settles back into the void left by the explosion, causing the ship's hull to "sag" under its own weight.

torpedo damage
Torpedo damage to the British merchant vessel Samtucky, circa 1944. Source: u/Gnome-de-Plume/Reddit

Finally, the void left from the explosion is filled with water once again, eventually creating a large geyser-like formation at the surface of the water. This causes the ship's hull, now sagging, to be bent upwards once again.  All of this happens in a matter of seconds. 

The stresses caused by this lifting-sagging-lifting process are usually enough to fatally damage the ship's keel. Perhaps even enough to cut the ship in two. If, however, the ship does manage to survive the encounter, it will likely be severely damaged and in need of urgent repairs.

Pretty terrifying. 

How do ships protect against torpedoes?

For merchant ships, there is little, if anything, in the way of defense against torpedoes. Since their primary role is for commercial activities, most of the ship's design is given over to things like fuel efficiency and carrying capacity. During the Second World War, merchant ships tended to travel in convoys that might be protected by submarines or warships, to take advantage of safety in numbers – a bit like a herd of animals. 

Beyond that, direct hits by torpedoes were often, but not always, fatal to the ship.

Warships, on the other hand, do have some self-defense options when targeted by a belligerent torpedo-carrying vessel. Beyond anti-submarine warfare (i.e. finding and neutralizing an enemy submarine), the ship itself also has various defenses and countermeasures available to it. 

Modern warships can use a combination of helicopters and sonar tracking to detect an incoming torpedo and take evasive actions. They can also make use of anti-torpedo torpedoes to intercept and destroy them before they become a threat to a ship.

Some of the most modern interception techniques include special missiles, designed to destroy torpedoes at a distance like the Surface Ship Torpedo Defense system (SSTD) currently under development by the U.S. Navy. 

Other options include deploying a towable torpedo decoy behind the ship, like the AN/SLQ-25 Nixie. These devices make noises that are louder than the ship's own propellers, in an attempt to confuse the onboard homing devices of an incoming torpedo. 

However, should any and all countermeasures and interception attempts fail, warships have some other adaptations to minimize the damage from a torpedo. In the past, ships could be equipped with physical protections like torpedo nets or torpedo bulges (fitted or retrofitted water-filled sponsons on the sides of a ship's hull). Both were a form of passive defense against torpedoes but were not foolproof. 

ship torpedo defenses bulge
HMS Glatton in drydock exposing her torpedo bulge, circa 1914-1918. Source: Surgeon Oscar Parkes/Wikimedia Commons

Another adaption, similar to torpedo bulges, was something called a torpedo belt. Common between the First and Second World Wars, it consisted of series of lightly armored compartments that extended along the ship's flanks at the waterline. 

The idea was that these compartments could absorb torpedo explosions (or artillery shells) that strike below the waterline, thereby minimizing the damage to the rest of the ship from the explosion. 

After the conclusion of the Second World War, the widespread use of aircraft (especially jets), and missiles, as well as improvements in command fire control effectively rendered these forms of passive protection obsolete. 

They are especially ineffective against modern "smart", deep-diving torpedoes, like the Mark 48, that are designed to detonate under a ship's keel. 

So, now we know what an icebreaker is, and what makes them so special, it is time for the main event...

Can an icebreaker survive a torpedo?

Not to sound flippant, but it really depends.

It depends on the type of torpedo (contact or proximity), and where the torpedo hits. If it detonates under the ship's keel, the icebreaker probably stands very little chance of survival. These kinds of torpedoes are, after all, designed to take out even the most heavily armed, and armored, of modern warships. 

icebreaker versus torpedo
Source: 海上自衛隊/Wikimedia Commons

Given the task these ships are designed to perform, their keels do have some special modifications (like additional cross members) to deal with the additional stresses and strains. However, it is unlikely that even these modifications would be enough to resist the power of a modern torpedo detonation. 

That being said, for contact detonations along an icebreaker's hull, an icebreaker may actually have a fighting chance. 

As previously mentioned, icebreakers' hulls are specially reinforced, especially at the bow, prow, and waterline, and could, potentially, survive a torpedo hit. The ship's design may also help cushion the blow as they are designed to "ride" over ice which puts immense strain on the ship's hull.

Their main hulls also tend to be "double-hulled" and are made of a special grade of steel that does not lose strength in very low temperatures. Icebreakers also tend to have specialized compartmentalization in their hulls to prevent excess flooding should a breach occur. 

These kinds of modifications are akin to torpedo belts and bulges adopted by warships in the early- to the mid-20th century.

icebreaker versus torpedo
Source: Tony Evans/Flickr

Icebreakers also have specially designed ballast control systems that enable partial flooding of the hull to change its center of mass. So long as these pumps are not knocked out by a torpedo, it is conceivable that they could be used to help prevent fatal flooding, or capsizing, of the ship, should it be hit by a torpedo. 

However, it bears repeating that icebreakers are not warships, and while they are heavily modified for ramming through thick ice, this is very different from being hit by a torpedo.

In the highly unlikely event that an icebreaker is targeted by a torpedo, its survival will be a mixture of luck and the complex interplay of stresses and strains on her hull should she be hit. 

If the torpedo is of a deep-diving, under-keel explosive type, the ship's fate is likely sealed. For more traditional direct-impact torpedoes, if an icebreaker is hit on the prow, chances are the ship will be able to limp back to port.

If hit on her sides, or rear, the ship may struggle to survive the impact, but it is not a foregone conclusion.

Or is it? We'll let you decide. And if it happens, we'll be sure to tell you all about it.

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