When Tiny Sharks Took Down U.S. Submarines

In the midst of the Cold War several U.S. submarines were forced to abandon their missions after sustaining damage. Was it a new Soviet weapon? Or were there more natural forces at play? 

Examples of damage done to submarines.

Disabled Submarines

During the Cold War the U.S. had a major problem affecting its submarine fleet, their sonar systems were being compromised. The neoprene sonar domes were sustaining cuts and scrapes that allowed the oil inside to leak out and sea water to seep in, making it virtually impossible for them to navigate while submerged. Some subs were also experiencing similar cuts to electric cables that hindered many other functions. The U.S. admitted that in the 1980s 30 submarines had to return from missions for repairs due to these damages. 

As to be expected, military leaders were concerned and many were afraid the Soviet Union had developed a new undetectable weapon. However, unbeknownst to them, the Soviets were experiencing the exact same problems with their submarines. Military scientists, engineers, and contractors quickly worked to discover the issue. 

A thick rubber dome with a chunk taken out of it by a cookie cutter shark. Photo courtesy of the Australian Museum

Cookie Cutter Sharks 

The cookie cutter shark is a parasite and belongs to a classification of sharks known as squaliformes that share this characteristic. They live in deep water where sunlight does not reach, though they will feed in shallower waters at night. Bucking the average person's idea of sharks, they are pretty small and only reach a maximum length of around one and a half feet (46 centimeters). They may appear quite drab being a light brown color with a darker brown band around their gills, but they are actually the brightest shark in the ocean. Their whole body, with the exception of the dark brown band, is covered in photophores. These let off a greenish phosphorescent light that attracts their prey in the dark depths. 

A cookie cutter shark. Photo courtesy of James Miller

Being parasites they feed off of larger animals without actually killing them, and accomplish this in a somewhat gruesome way. When a larger fish or mammal is attracted by the phosphorescent light the shark will use its hook-like upper teeth to latch onto it. The shark will then create a suction with its mouth and use its lower teeth, which are often described as resembling a band saw, to cut out a chunk from its prey. The chunk is usually only about two inches wide and two and a half inches deep, and is almost never fatal. This is evidenced by the fact that whales, sailfish, and other large aquatic creatures have been observed with dozens of scars from multiple cookie cutter attacks. 

A closeup of cookie cutter shark teeth. Notice how the lower teeth resemble a saw blade. Photo courtesy of the Australian Museum

Discovery and Solution

As the military searched for what was causing the damage to their submarines they found out that undersea cables and scientific oceanographic equipment was also experiencing the same type of attacks. Though the cookie cutter shark was known to science it lived at such deep depths that there were very few examples of them. It was almost through sheer luck that scientists made the connection between them and the damage suffered by undersea equipment. 

A piece of rubber tubing that was sawed on by a cookie cutter shark. Photo courtesy of Richard Dashnau

The most widely accepted theory is that the cookie cutters believed the submarines to be large whales and latched themselves onto the softest parts, these of course being the sonar dome and rubber cables. Once the culprit was finally discovered the Navy came up with a simple solution. The neoprene sonar domes and any other soft components were encased in fiberglass that the sharks could not chew through.

A dolphin with a cookie cutter shark bite. Public Domain