Various marine warfare activities constitute a series of threats to the marine environment, the most serious one being the SNS, the strategic nuclear submarine. Nuclear-powered submarines and surface ships routinely release a certain amount of radioactivity into the sea; the quantity is relatively insignificant, when compared to the potential contamination that could result from an accidental or intentional sinking. The long-lived isotopes produced in a reactor build up while a submarine is in continuous operation. If a nuclear submarine were to sink after about fifty days of continuous operation, it could contaminate the sea with long-lived radioactivity equivalent to what a twenty-kiloton atomic bomb would release (the Hiroshima bomb was thirteen kilotons). This calculation does not account for the possibility that nuclear warheads aboard the vessel could be detonated or that, in the case of an intentional sinking, nuclear-armed torpedoes or missiles might have been the enemy's offensive weapon.
Other effects of warfare on the undersea world are: (a) Undersea explosions These take a serious toll on marine animals, especially ray-finned bony fish, which comprise about 95% of the fish in the sea. The air bladders of these fish are easily ruptured by underwater explosions. In addition, some of the materials used in explosives are poisonous. (b) Oil A threat is posed by the enormous increases in tanker size since the 1940s, and the emplacement of vulnerable offshore oil platforms around the world: oil contamination of the sea could be significant in a major war. (c) Herbicides As a result of massive herbicide spraying of mangrove forests along the coast of South Vietnam during the Vietnam War, coastal habitats were devastated. Scientists surveying offshore areas found that the loss of these marine nurseries and breeding grounds had caused a severe decline in the populations of fish, planktonic organisms, and shellfish. Recovery, they estimated, could take more than a hundred years. (d) Testing of nuclear weapons Since the 1940s these have been associated directly with the sea. More than 1,000 nuclear bombs have been detonated; of these, 373 were exploded in the atmosphere (about 80% of the long lived components of these blasts probably reached the sea), 35 were exploded along the sea surface, and 6 were detonated undersea.
The importance of the ocean to military strategists is actually on the increase. Since the 1960s there has been a significant acceleration in the growth rate of the fleets operated by the world's 51 navies. Naval stocks - a measurement combining the number of vessels, their tonnage, and their military capabilities - have doubled since World War II. There are presently about 2,300 large and small naval vessels afloat and about 260 large nuclear submarines in operation (about 240 of them USA or Russian). As this fleet expands, the possibilities for accidents multiply. At least six nuclear-powered submarines have been lost. Two US nuclear subs have sunk in the Atlantic (the Thresher in 1963 and the Scorpion in 1968), and it is believed the Soviets lost as many as four between 1968 and 1971, two in the Atlantic, one in the Mediterranean, and one in the Pacific.
If a major nuclear war erupts, the instruments of greatest violence will probably emerge from the sea. The effects of wartime nuclear contamination in the sea could be devastating. Long-lived radioactive products would be distributed by ocean currents throughout the sea. Several of such products are taken up by marine organisms and distributed through the food web, especially strontium-90 (which follows the same course in organisms as calcium) and caesium-137 (which acts like potassium). Plutonium is also taken up by many marine organisms, some of which concentrate it to levels from a thousand to as much as ten thousand times higher than its initial concentration in seawater.